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Spring Fever Spreading

Will Spring be on time for your region? Join the Conversation >> Long Range Spring Outlook

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A rather unusual setup for this time of year looks to unfold in the first week of February.

A massive pattern flip in every sense of the phrase is going to happen. A system will form on the lee of the Rockies around February 3 and cut through the Great Lakes, perhaps making for a small risk for severe weather. However, it looks like the cold front will stall out within this region before another system forms off the Rockies as the longwave trough pushes east. By the time the final cold front pushes through, the areas south of where the cold front stalled out will have been under 150 hours, or almost 7 days of southerly winds... so, needless to say, there should be more than enough moisture.

The February 3 system is found off the coast of Maine in this image. The cold front has stalled and is beginning to turn into a warm front. Already upper 60 dew points along the inland coast and you can see Lee Cyclogenesis beginning in southeast CO. This sequence of events and setup here is often what proceeds big severe events.

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The system forms and begins to push east. 

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Euro has a different picture. There's no centralized low pressure. I'm not aware of many significant wintertime events that have no centralized low pressure, though I don't doubt there are some. But looking at the surface winds, there are 2 areas of convergence with backing surface winds. Due to the lack of a strong low pressure, the lowlevel winds are weak and would certainly be an inhibiting factor for the tornado threat. One big thing that's concerning about Euro is how significantly the instability jumps from 00z to 06z... in other words, after the sun sets. This is the region that gets struck by nighttime events the most, and this would suggest this may be a nighttime event.

The relatively weak speed shear (i.e., wind speeds that increase with height) is in better proportion to the amount of instability than if you were to have a very strong system. In general, a good balance of instability and speed shear can result in longer-lived supercells (this is the purpose of the Bulk Richardson Number) that may or may not result in tornadoes. Too much shear and it collapses the tower, resulting in a squall line. Too much instability and it rains itself out like a summer popup storm.

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A few things to watch for in the coming week..

1) How far south the cold front from the first system goes before it stalls. Stalls like it's currently forecast, there's gonna be more moisture, and in turn a higher severe threat. If it goes further south than this, then the severe threat won't necessarily be gone, but it'll be confined closer to the coast. I'd call this the biggest bust potential.

2) The strength of the second system's low pressure. GFS's solution with the strong low pressure would create a higher severe threat. Euro's solution would also create a severe threat, though not as high... especially not as high of a tornado threat.

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Can such a significant rain event for a prolonged period of time followed by a cool down cause more favorable conditions for snow if a storm tracks this way? 

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1 hour ago, Gator said:

Can such a significant rain event for a prolonged period of time followed by a cool down cause more favorable conditions for snow if a storm tracks this way? 

If you're asking if the frozen moisture left over from the rain event can cause a more favorable setup for snow, I would say no. 

The argument about how a fresh snowpack can help suppress the storm track and make the area more favorable to be in the wintry side of a system is based on differential heating and the fact that systems like to follow baroclinicity. 

Since a fresh snowpack is white, which is very reflective (high albedo), it'll cause incoming radiation to be mostly bounced back to space, which keeps the temperatures low. Since snowpacks typically have a sharp gradient, there's a region of medium-to-low albedo next to a region of high albedo, which creates temp gradient. Low pressure systems feed off temp gradients/baroclinicity, so they'll want to follow that gradient assuming nothing forces them to make a detour... like a strong high pressure.

I doubt frozen moisture leftover from a rain event would be reflective enough and/or create enough of a temp gradient to make this phenomenon happen. Leftover moisture preceding a sudden freeze usually just creates black ice which is almost invisible, so unless there was a solid layer of ice for hundreds of miles, I don't think so.

Not to mention this whole thing gets messed up when there's cloud cover since there's low incoming radiation anyway.

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Both models mostly held their ground... though Euro comes in with stronger low-level winds. The low-level moisture is really pretty impressive for early February.

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GFS comes in with a weaker system, weakening speed shear. Instability is only marginal verbatim, but GFS is known to underestimate instability so the fact that it's showing 700-1000 j/kg of CAPE doesn't concern me that much.

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Euro got serious quick. The low pressure is stronger than GFS and further north. The severe threat here would start in Arkansas and then spread northeast into the lower Ohio Valley, targeting from Little Rock to Paducah to Louisville, and perhaps Cincinnati and Columbus if a squall gets going. Tornado threat would be maximized in the mid-Mississippi valley... Little Rock, Memphis, and Paducah. Supercells would be the probable initial storm mode since there's a dryline in eastern Oklahoma. Speed shear is strong... directional shear isn’t the best... with surface winds out of the south-southwest.... but it’s good enough.

 

 

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You know there's a dryline here from 2 ways... the first is from the surface winds, which I haven't shown. The winds behind the dryline in this case are almost purely west-southwesterly, straight from New Mexico. Second is the temperatures behind the dew point gradient in eastern Oklahoma. You have that sharp dew point gradient but the surface temps actually get slightly warmer behind the dryline, which is common and a telltale sign of a dryline because this would never happen with a cold front. In fact, the cold front is actually still oriented parallel to the OK/KS border while the dryline is in eastern Oklahoma. You can see the cold front's dryer airmass in the dew point map... the cP airmass is actually less dry (higher dew point) than the desert airmass. 

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GFS has clearly trended to a more amplified and southern first system which appears to be a cave-in to Euro. Let's see if this leads to a higher or lower severe threat.

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Second system is further south, and again, weak. The environment just ahead of the dryline/cold front merger is pretty modest. There's a low-level backing profile which will mess with severe potential. But there appears to be a pre-frontal trough kind of feature in the warm sector that is causing a more favorable wind profile. Looks like GFS has some storms popping in this area and would probably make southern Alabama and southern Mississippi the greatest severe threat. Just like Euro though, there's going to be a dryline in at least east Texas, which will make this the first dryline event of the year.

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CIPS analogs for this time frame indicate a classic western trough and SER setup. While severe probabilities are certainly greater than climatology for these thread dates, the severe probability on the analogs is not much to get excited about. Seems like a quasi-stationary front could be in the works and when combined with the SER and high PWAT values suggests flooding in the OHV and lower MS valley could be more noteworthy than the severe thunderstorm threat. I didn't include images, but CIPs analogs indicate widespread 2-3" amounts across the lower OHV.

Spoiler

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3 hours ago, StL WeatherJunkie said:

CIPS analogs for this time frame indicate a classic western trough and SER setup. While severe probabilities are certainly greater than climatology for these thread dates, the severe probability on the analogs is not much to get excited about. Seems like a quasi-stationary front could be in the works and when combined with the SER and high PWAT values suggests flooding in the OHV and lower MS valley could be more noteworthy than the severe thunderstorm threat. I didn't include images, but CIPs analogs indicate widespread 2-3" amounts across the lower OHV.

  Hide contents

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Yeah I do like using CIPS and I do see that there's low number of analogs with severe weather--even for this time of year--but I'm cautious of it since for 2 reasons

First is that it looks at 105 analogs. There more than likely isn't 105 unique cases that have looked like this in this time period. There's likely several cases of multiple consecutive days, which would make severe weather look relatively insignificant because with a pattern like this in this time of year, only one of those days will produce the bulk of the severe weather.

Second is that there wasn't much agreement among GEFS ensembles in the 29/00z run... I guess that's needless to say for 200+ hours out.

GFS started with the higher severe threat, then Euro caved to that... then GFS changed and weakened the low, now Euro has the higher threat. So we'll have to wait and see if this game of chase continues or maybe GFS is getting cocky.  But with dew points in the mid-upper 60's in February, it's hard not to get severe weather... which I know is not what you're saying. And you're right, with the PWATs as high as they are, some flooding is certainly a real possibility even though it seems to be a relatively progressive system. I'm thinking the highest threat for that is in Mississippi and Alabama.

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The first system has trended stronger and further north for 4 runs now... now it's bringing rain to Canada. Sheesh.

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Stronger system implies more moisture return... but maybe also more CAA, thus, cold front further south? 

Edit: another weak system, but managed to come further north than the previous 2 runs.

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Is this an anomaly for the beginning of Feb or is this a sign of a warming trend / possible early spring? 

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7 minutes ago, Gator said:

Is this an anomaly for the beginning of Feb or is this a sign of a warming trend / possible early spring? 

Neither to be honest. January is typically the quietest month for severe weather, and though winter severe events are rare, they become more common as you move into and through February. The climatological severe weather minimum was on December 30, so severe weather is statistically becoming more prominent--though it depends on the year of course. 

I haven't done the research but I doubt there's any correlation between an early February severe event and warming trend/early spring. If the entire month stays like this then that'd be a different story.

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SPC has begun mentioning this time period. Haven't introduced any probabilities but with GFS trending toward Euro I'm sure it won't be long. Euro continues to show the higher severe threat, GFS is more modest. I'm leaning toward Euro with moisture and instability because GFS sucks for that. I haven't posted here much because a severe threat may be increasing for the Midwest so that intrigued me.

Quote

 Day 4-8 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0228 AM CST Thu Jan 31 2019

   Valid 031200Z - 081200Z

   ...DISCUSSION...
   Models are in general agreement through the day3 period allowing
   Arctic air associated with a deep upper low to shift east across the
   Midwest/Great Lakes region into New England where it should slowly
   modify. A more progressive pattern is expected to evolve into the
   middle portions of next week with significantly more upper troughing
   expected in the mean across the western US. One notable short-wave
   trough is forecast to eject across the central Plains into the mid
   MS Valley by the end of the period. While some moisture will return
   ahead of this feature, forecast instability is not expected to be
   adequate for organized severe.

   Beyond day4, considerable variability exists among the models
   regarding multiple ejecting short waves across the southwestern US
   toward the middle of the country. During the day5-6 time frame
   higher-PW air mass will likely return across east TX into the
   western TN Valley. There is some potential for significantly more
   unstable air mass to evolve by mid week that could support organized
   severe convection. Given the uncertainty of aforementioned short
   waves, timing and placement of these features will largely modulate
   organized convection. At this time predictability is too low to
   warrant 15% severe probs; although the pattern appears to be
   evolving such that some severe threat may ultimately materialize.

 

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1 minute ago, ClicheVortex2014 said:

How is there this much of a change in one model run, 6 days out?! This is huge.

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Been busy. Looks like this has potential to be at least a low-end event for a relatively large area. As usual, GFS is lacking in moisture. 

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@ClicheVortex2014 I must say, absolutely stellar write ups. I'm not all that well versed with severe weather, but those write ups helped me to understand alot. Great job and thank you. 

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23 hours ago, Uscg ast said:

@ClicheVortex2014 I must say, absolutely stellar write ups. I'm not all that well versed with severe weather, but those write ups helped me to understand alot. Great job and thank you. 

Thank you very much! I appreciate it. 

This severe threat has really pushed west from a few days ago. GFS is further east... NAM is further west. Speed shear is pretty good... directional shear is good enough with southerly surface winds and west-southwesterly 500mb winds. Instability is the main thing disagreed about. Something the two models both agree on is the weak low-level winds which should hold down the tornado threat a bit.

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SPC says a squall should form pretty quick but strengthening shear throughout the day should be enough for some QLCS tornadoes. Low-level shear doesn't look that extreme, so I don't think this is a dozen tornadoes kind of event, but you never know. Either way, definitely a reminder that spring is approaching.

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18z HRRR showing multiple rounds of thunderstorms... as SPC said, shear increases through the day, becoming extreme through the night. Nothing on this HRRR run stands out as impressively organized/long-lived. If there are any supercells, they're transient. But this is the fantasy range for HRRR, so it could look more serious.

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I assume this is the beginning of the evolution of the squall. 

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Pretty impressive warm sector for being 24-36 hours away from the main event. We're just lucky there's not better timing and it doesn't take a negative tilt because this is the kind of look that precedes major events.

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5% tornado 15% wind

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Quote

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1136 PM CST Tue Feb 05 2019

   Valid 061200Z - 071200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM NORTH-CENTRAL
   TEXAS THROUGH THE OZARK PLATEAU AND INTO THE LOWER OHIO VALLEY...

   ...SUMMARY...
   A couple of severe thunderstorms may occur Wednesday afternoon, but
   should become more probable after dark from the southern Plains into
   parts of the Ozarks and lower Ohio Valley.

   ...Synopsis...
   Broad upper trough currently covering much of the western CONUS is
   expected to become more progressive today, moving from its early
   period position over the Intermountain West into the Plains by 12Z
   Thursday. Southwesterly flow aloft from the Southwest through the
   central and southern Plains which has been in place for the past two
   days will persist another day today, strengthening with the approach
   of the upper trough. Guidance is in good agreement that 500 mb wind
   speeds will exceed 100 kt after 00Z from the southern High Plains
   through the central Plains as an embedded shortwave trough rounds
   the base of the upper trough and ejects through the central/southern
   High Plains.

   Thunderstorms, including the potential for severe storms, are
   expected to evolve in two fairly distinct regimes. The first is from
   this afternoon through the evening within the warm conveyor from
   eastern OK into the mid MS/lower OH Valleys. The second is later
   tonight primary across the southern Plains along the cold front.

   ... Eastern OK into the mid MS/lower OH Valley this afternoon
   through this evening...
   Stationary front currently extending from a surface low centered
   near SPS northeastward into northwest AR and then east-northeastward
   into central KY is expected to remain largely in place throughout
   the first half of the period. Strengthening mid-level flow into this
   boundary as well as the likelihood for one or more embedded,
   low-amplitude shortwave troughs leads to the expectation for
   increased thunderstorm coverage during the early afternoon. The
   strongest storms will likely develop over south-central/eastern OK
   where instability will be a bit greater. Mid-level winds will be
   strong, supporting a quick storm motion (cloud-layer mean wind will
   be over 55 kt) and robust vertical shear (0-6 km bulk shear near
   65-70 kt). Potential for damaging wind gusts and perhaps even a
   brief tornado exists as these storms interact with the warm front,
   which will beginning moving slowly northward during this time. Some
   marginal severe hail is also possible. Primary limiting factor is
   instability, which will be tempered by as a result of widespread
   cloudiness and stunted daytime heating.

   ...North TX/Central OK into western AR overnight...
   Much of this region is expected to be free of deep convection from
   the late afternoon through the evening. However, the overall
   evolution of the upper trough, and the progression of embedded
   shortwave trough in particular, will encourage a
   eastward/southeastward surge of a strong cold front across the
   southern Plains. Air mass ahead of the cold will have stabilized
   somewhat in the wake of earlier storms but strong forcing for ascent
   combined with the remaining marginal instability (supported
   primarily by dewpoints in the low to mid 60s) is expected to result
   in the development of a convective line. Vertical shear is more than
   supportive of storm organization but the fast motion of the front
   (and resultant undercutting) and limited instability cast
   uncertainty towards just how organized the line can become. Even
   with this uncertainty, potential for strong wind gusts and perhaps a
   few tornadoes is high enough to merit slight-risk-equivalent tornado
   and wind probabilities from north-central TX into northwest AR.

 

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Are there any tools / radars for newbs like myself that just want to look for tornadoes in the area? Maybe even some type of warning system via twitter or other social media? Moving from Florida to Middle Tenn, my only worry is tornadoes. I'll take a hurricane all day lol. Tornadoes scare the crap out of me. 

Edited by Gator

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3 hours ago, Gator said:

Are there any tools / radars for newbs like myself that just want to look for tornadoes in the area? Maybe even some type of warning system via twitter or other social media? Moving from Florida to Middle Tenn, my only worry is tornadoes. I'll take a hurricane all day lol. Tornadoes scare the crap out of me. 

At the most basic, I'd suggest either Wunderground radar and/or Twitter (watch hashtags such as #wxfl or #wxtn)... though the latter really depends on the magnitude/scope of the event. Wunderground is kinda outdated but it can get the job done. I'd highly suggest purchasing Radarscope though... it's an app on your phone that's a one-time purchase of like $5 I think. Its easy accessibility makes it popular among weather enthusiasts and pros. It has a lot of features from basic to advanced. It also has a feature that can show your location on the map so you can have some sense of relativity. It may take a minute to get familiar with the product but it's not too hard. I've had it for 2 or 3 years now and I still use it regularly.

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Watch out for the outflow boundary

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Quote

Mesoscale Discussion 0076
   NWS Storm Prediction Center Norman OK
   0341 PM CST Wed Feb 06 2019

   Areas affected...southeast Oklahoma...extreme northeast Texas
   through central Arkansas

   Concerning...Severe potential...Watch possible 

   Valid 062141Z - 062345Z

   Probability of Watch Issuance...40 percent

   SUMMARY...Some increase in thunderstorm intensity and organization
   might occur during the next couple hours. Primary threats appear to
   be isolated damaging wind hail, but a tornado or two cannot be ruled
   out. Overall threat appears somewhat conditional in the near term,
   so a WW issuance will ultimately depend on convective trends.

   DISCUSSION...As of mid afternoon a quasi-stationary front extends
   from southeast OK through northwest AR into southeast MO. South of
   the front, an outflow boundary extends from the AR/TN border
   westward through central AR. South of these boundaries a few cloud
   breaks have resulted in modest destabilization of the warm sector
   with 500-1000 J/kg MLCAPE. This destabilization process has resulted
   in some increase in intensity of thunderstorms from southeast OK
   into central AR. Wind profiles show ample (60+ kt) vertical shear
   through a deep layer, however, size of low-level hodographs has been
   limited so far by veered low-level winds. This environment may
   support a few organized structures including isolated supercells and
   bowing segments with main threats being locally damaging wind gusts
   and hail. However, primary limiting factors appear to be weak
   forcing aloft and a tendency for a capping inversion to build as
   warmer temperatures in the 850-700 mb layer advect northeast.

 

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