Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 02/06/21

Area Forecast Discussion
National Weather Service Duluth MN
532 PM CST Fri Feb 5 2021 .DISCUSSION...(This evening through Thursday) Issued at 337 PM CST Fri Feb 5 2021 A prolonged relatively dry but very cold period is in store across the Northland with Wind Chill Advisories and Warnings needed through much of the forecast period. Cold air will continue to move into the region tonight with 850MB temperatures dropping to around 30 below zero Saturday. High pressure will remain off to the west keeping a decent gradient in place which will keep the wind up tonight into Saturday, from 8 to 15 mph with higher gusts. Cloud cover hasn`t been too widespread this afternoon and we expect some decrease tonight which will help allow temperatures to drop. There may be some stronger katabatic winds again tonight along the North Shore as seen in the HRRR and RAP. We went into the 75th percentile for winds there which gave gusts 35 to 40 mph. There could be some locally higher values as well. We kept Wind Chill Advisories for all areas tonight, a few spots in far northern Minnesota will touch 40 below and if it appears to be more widespread, a Wind Chill Warning may be needed. We have POPs along portions of the South Shore tonight due to the cold west/northwest low level flow. The airmass is dry but very cold and at least some flurries shouldn`t be too hard to produce. We don`t expect much for accumulation and the HREF agrees with only light amounts from the Bayfield Peninsula through Hurley and Gile. A shortwave will aid in bringing in the colder air Saturday and may produce some clouds and flurries, mainly over northern Minnesota. The cold will be the main story through most of the period and we extended the Wind Chill Advisory through Sunday for northern Wisconsin and Pine County in Minnesota. However, values may rise above advisory thresholds for a time during the afternoon but it will remain quite cold. For portions of northern Minnesota the advisory was extended into next Tuesday. Far northern Minnesota will see the coldest temperatures and enough wind to produce wind chills lower than 40 below. We issued a Wind Chill Watch there from Saturday evening into Tuesday. We expect that period to feature wind chills lower than 40 below at night with them rising during the day but remaining at least at advisory thresholds. The cold looks to stick around well into next week, and Wind Chill Advisories/Warnings may be needed beyond Tuesday. Monday night will have to be watched for some very cold lows, 30 below to around 40 below, over far northern Minnesota. The high noses further into the region which will weaken the gradient some and may allow for more areas to decouple. However, the guidance is mixed at best in forecasting this with the GFS/Canadian showing a stronger gradient than the ECMWF. There also may be some cloud issues to deal with. Despite the very cold temperatures and high delta-T values, lake effect snow will not be a big threat over the next several days. This is due to the low level winds remaining too west of north limiting fetch. We did increase POPs along the Bayfield Peninsula toward Hurley/Gile tonight into Saturday but only have light accumulation each period over the next few days. && .AVIATION...(For the 00Z TAFS through 00Z Saturday evening) Issued at 532 PM CST Fri Feb 5 2021 Very cold air will continue to move into the Northland tonight into Saturday. A mix of MVFR and VFR clouds will occur through the period, with the MVFR ceilings most likely over far northern Minnesota and along the South Sore. There still will be some flurries or light snow as well as drifting/blowing snow this evening. Winds will diminish tonight but won`t become light as a stronger gradient remains in place. Overall, we expect clouds to decrease for most areas tonight but as often is the case in these cold airmasses, some MVFR or even isolated IFR ceilings will be possible in spots. The clouds will hang around the longest in far northern Minnesota and along the South Shore. Strong wind gusts will be possible along the North Shore tonight as well due to katabatic winds. A shortwave may bring some flurries/light snow on Saturday to portions of the Northland but little accumulation is expected. && .PRELIMINARY POINT TEMPS/POPS... DLH -14 -5 -21 -6 / 10 10 10 0 INL -18 -10 -25 -10 / 10 10 10 0 BRD -11 -4 -20 -5 / 10 0 0 0 HYR -10 1 -21 -3 / 10 0 0 0 ASX -8 0 -15 -2 / 40 30 20 10 && .DLH WATCHES/WARNINGS/ADVISORIES... WI...Wind Chill Advisory from midnight tonight to noon CST Sunday for WIZ001>004-006>009. MN...Wind Chill Watch from Saturday evening through Tuesday morning for MNZ010>012-018>021-026. Wind Chill Advisory until 8 PM CST Saturday for MNZ010>012- 018>021-026. Wind Chill Advisory until noon CST Tuesday for MNZ025-033>037. Wind Chill Advisory from midnight tonight to noon CST Sunday for MNZ038. LS...None. && $$ DISCUSSION...Melde AVIATION...Melde
Area Forecast Discussion
National Weather Service Fort Worth TX
704 PM CST Fri Feb 5 2021 ...New Short Term, Aviation... .SHORT TERM... /NEW/ Update: Only adjustments from the midday short-term discussion below was to increase west and northwest winds by Saturday afternoon. Deep mixing initially in behind the exiting surface low and prefrontal trough will promote increasing westerly winds 15 to 20 mph. Increasing low level CAA behind the mid afternoon cold front and a strengthening pressure gradient will drive even stronger northwest winds 15 to 25 mph with gusts 30 to 35 mph. We may reach borderline Wind Advisory Saturday afternoon, so this will need to be monitored closely. Look for winds to veer northerly and decrease to between 10 to 15 mph after nightfall Saturday evening. Regarding precipitation with the next mid level impulse Saturday, it still appears the best lift and moisture will be confined to East Texas and the Ark-La-Tex. Instability looks marginal at best, so kept any isolated potential for lightning strikes out of the forecast and kept best rain chances confined to our northeast counties. A rogue shower or two can`t be ruled out across the eastern counties as far back west as the eastern DFW Metroplex. 05/ Previous Discussion: /This afternoon through Saturday/ Large scale subsidence will increase behind a departing shortwave this afternoon, resulting in decreasing clouds and an end to rain chances. After a cold start to the morning with lows in the 30s and lower 40s, temperatures will slowly warm through the afternoon, reaching highs in the 50s and lower 60s. The return of low level moisture tonight in response to a deepening lee trough across the Central and Southern High Plains will result in the return of low clouds along with slightly warmer temperatures. Lows tonight will range from the upper 30s to the lower 40s. Another cold front will move across the region on Saturday, bringing a reinforcement of dry and cool air along with a breezy west to northwest wind Saturday afternoon. The breezy and dry weather will result in an elevated threat for grass fires, especially across the far western zones. A few locations in the west could also briefly touch Wind Advisory criteria behind the front, but the windy conditions will be brief and on the low end of criteria. Cold air advection Saturday afternoon will be offset but ample sun and some adiabatic warming, therefore, highs should still manage to reach th upper 50s and 60s in most locations. The only exception will be the northeast zones where clouds will linger the longest. 79 && .LONG TERM... /Issued 323 PM CST Fri Feb 5 2021/ /Saturday night through Next Friday/ The main story of the long-term forecast is to continue to monitor the arctic cold airmass that will expand southward next week. But first...let`s enjoy the nice/mild temperatures Sunday and Monday. A surface ridge will move over the region Saturday night, shifting our winds to the southeast by Sunday morning. The combination of light winds and clear skies will result in overnight temps in the 30s. Many locations across North TX will see temps below freezing Sunday morning. Temperatures will warm into the mid 50s and 60s in the afternoon, with a few locations reaching low 70s across the far western counties. Expect another mild/warm day on Monday with some areas across Central TX warming into the low-to-mid 70s ahead of the next system. The next front is set to arrive Monday evening or Tuesday morning, bringing the first round of cold air to the region. There`s a low chance for a few light showers Monday afternoon and night mainly across the northeast where the best convergence of moisture and lift will exist. The high temperatures on Tuesday will stay in the 40s and low 50s across North TX, to 50s and 60s across Central TX. Another shot of arctic cold air will push southward mid-to-late week. Despite the large uncertainties on how much moisture will be available for any winter precipitation, this pattern will definitely support some very cold temperatures. Most of the medium and long range guidance continue to support a negative phase of the North Atlantic Oscillations (NAO) during this time period, which will allow the Canadian and arctic cold air to move south. If this forecast verifies, we will be looking at temps 20+ deg below normal with highs in the 30s to low 40s and overnight lows in the teens and 20s on Thursday/Thursday night and Friday. What we all want to know is...will we get any wintry precipitation? The way things look right now it appears that this system will bring a chance of a wintry mix across most of North & Central TX on Thursday-Friday. The deterministic GFS continues to be more aggressive in bringing some wintry precipitation, as it keeps showing the highest overrunning moisture over our area. While the ECMWF keeps most of the activity north and west of us, many of the ensemble members do show a southern track of the shortwave. When compared to our climatology, this type of pattern (North American Trough) has been associated with very cold temperatures, but limited moisture. Still, there has been cases where just the right amount of moisture was available to produce wintry precipitation. All we can do now is keep monitoring the trends as the forecast will definitely change as we get close to this time period. Sanchez && .AVIATION... /NEW/ /00Z TAFs/ Challenges: Arrival of MVFR cigs below 020 and potential southwesterly LLWS within the PBL. VFR conditions and southeast winds 10 to 15 knots will be the rule, as lee-side cyclogenesis deepens across E NM and slowly moves east-southeast into the TX Panhandles/NW TX region overnight. S-SW flow within the PBL is expected to increase to between 30 to 40 knots during the pre-dawn hours. These strong southerly winds just above the surface will help draw rich moisture from the Gulf of Mexico northward and into the area between 08z-12z Saturday morning. MVFR cigs mostly between 1300-2000 feet are expected to impact Waco by 08z-09z Saturday before arriving at D10 terminals in the DFW Metro by 12z Saturday. Moisture progged by RUC soundings looks fairly deep (~ 1500 feet deep), thus MVFR cigs will likely hold over all terminals until late Saturday morning. The strong S/SW PBL winds and less intense SE surface winds during the predawn hours may present a brief period of LLWS just before 12z. Confidence is too low at this point to insert into the forecast. A surface low tracks east across the D10 area with veering low level flow and drier low level air by 18z and should help scatter any MVFR cigs out. Though a stray shower or two is possible near eastern DFW Metro terminals, I will maintain no mention VCSH in the forecast. Surface winds will veer W/SW 13-17 knots before going NW 15-20 knots with gusts between 25-30 knots with cold FROPA by 21z with the surface low moving east away from the area during the afternoon. Crosswinds may present some impacts at DFW International for mid morning through early afternoon, with earlier impacts on any diagonal runways being used due to ongoing construction main runways at the airport. 05/ && .PRELIMINARY POINT TEMPS/POPS... Dallas-Ft. Worth 40 59 34 61 46 / 0 5 0 0 0 Waco 40 66 34 64 46 / 0 0 0 0 0 Paris 37 50 31 54 38 / 0 40 0 0 0 Denton 37 58 30 61 43 / 0 10 0 0 0 McKinney 37 57 31 60 43 / 0 10 0 0 0 Dallas 42 60 35 63 47 / 0 5 0 0 0 Terrell 38 58 32 60 43 / 0 10 0 0 0 Corsicana 41 63 35 63 46 / 0 5 0 0 0 Temple 40 68 34 66 47 / 0 0 0 0 0 Mineral Wells 37 61 31 67 44 / 0 5 0 0 0 && .FWD WATCHES/WARNINGS/ADVISORIES... None. && $$
National Weather Service Hastings NE
922 PM CST Fri Feb 5 2021 ...Short Term Update... .UPDATE... Issued at 917 PM CST Fri Feb 5 2021 QPF and the resulting snow totals for tonight and Saturday morning were nudged down slightly to match trends on the latest runs of the HRRR and RAP. This takes the peak snowfall totals down closer to the 4-6" range. Otherwise, things appear to be mostly on-track. Radar returns are starting to blossom over western portions of the area, and these areas should start seeing snowflakes shortly. It appears that the heaviest snow will occur roughly between 2am and 9am, and accumulating snow should end by noon on Saturday. && .DISCUSSION...(This evening through Friday) Issued at 416 PM CST Fri Feb 5 2021 So far this season we have generally been blessed with rather mild winter weather, but thats all about to change this week. This week could potentially be the harshest winter weather we have had thus far this season! There have been quite a few changes over the last couple of forecast packages, but thankfully that has been due to models coming in to better agreement. So as of right now there are really 4 main topics to cover: 1. First round of snow tonight and into tomorrow 2. Second round of snow tomorrow night and into Sunday 3. Third round of snow Sunday night 4. The Arctic blast and our dangerous wind chills So starting from the top with the first round of snow that is expected tonight. A broad upper level trof has been digging its way south over the Northern and Central Plains with a parent low situated over Ontario. This low and the short waves that move around it, are the start of our intense weekend and week ahead. Snow ratios, QPF, and snow totals have all been trending up over the last 2 forecast packages. Models have come in to better agreement as recently as this morning, with a nearly unanimous southward shift in the main snowband. The most difficult aspect currently is being able to nail down the location of this band. There is also likely to be a sharp gradient in snowfall totals due to this band, even one county apart could mean the difference between 2" and 5" for example. This is also expected to be a very fluffy snow, with the highest snow ratios being around 18:1 and 19:1. Nearly all of the short term models have been trending up in their pwat values and therefore their QPF as well. So even though it`s tempting to think that the current QPF estimates might be too high given how cold this system is, there seems to be enough evidence and model support to justify the current forecast. With the high SLRs and QPF, 5-7" of snow is expected to fall within the band and 1-5" is expected elsewhere. Winds will also create the issue of blowing snow and reduced visibilities with gusts expected to be around 25-30 mph. The second round of snow is expected tomorrow night and into Sunday morning. A quick little short wave dives south over our area while we remain in NW flow aloft. As cold Arctic air is funneled south snow ratios will remain high and it`s possible to get at least flurries out of nearly every perturbation that passes through. With this set up it really doesn`t take much to get some sort of snowfall. This second round (and the third round) are not expected to be nearly as intense as the first one tonight. However, even limited moisture can still produce several inches of snow due to the higher SLRs. With this second wave snow amounts look to be mainly between a Trace to 3" and mostly north of the NE-KS border. The areas that could see above an inch are mainly north of the I-80 corridor at this point, though that could change between now and then. The third round of snow comes Sunday overnight and is even less still. Once again being in NW flow aloft allows for even the smallest of waves to affect us, as is the case here. The coldest air really begins to settle in around Sunday night and so we could squeeze out an additional T-1" of snow with this little perturbation Sunday night. This particular one is probably the most uncertain of the three and a lot is still subject to change. But the main point is that over the next several days it will be very easy to have even just a little bit of snowfall. Now on to the fourth point, the real winter kicker...the blast of Arctic air that is being funneled south by this entire system. Temperatures will start to plunge tonight and tomorrow but continue to drop through Sunday and bottom out with highs in the low teens and single digits on Monday. Lows are expected to drop below zero starting Sunday night and will drop even further in the coming days. Unfortunately this air mass looks to stay in place for a while as the upper low oscillates over Ontario. Wind chills will be dangerously cold Sunday night onward, with the lowest values generally being around -15 to -25 degrees. The single digit and lower teens daily highs continue through the end of the 7-day forecast. This means our temps will be a good 20+ degrees below average for this time of year. && .AVIATION...(For the 00Z KGRI/KEAR TAFS through 00Z Sunday) Issued at 523 PM CST Fri Feb 5 2021 Snow will begin to move into the area after 06Z, becoming fairly widespread after 08-09Z. Ceilings are expected to be MVFR, with visibility below a mile at times. Snow will begin to let up in the 12-14Z timeframe, with ceilings likely eventually rising back to VFR in the afternoon. Winds will turn northerly early Saturday morning, with gusts to around 20kts. This will also lead to some minor blowing snow before winds taper off again in the afternoon. && .GID WATCHES/WARNINGS/ADVISORIES... NE...Winter Storm Warning until noon CST Saturday for NEZ046>048- 061>064-075>077. Winter Weather Advisory until noon CST Saturday for NEZ039>041- 049-060-073-074-084>087. KS...Winter Weather Advisory until noon CST Saturday for KSZ007-019. && $$ UPDATE...Mangels DISCUSSION...Shawkey AVIATION...Mangels
Area Forecast Discussion
National Weather Service Goodland KS
900 PM MST Fri Feb 5 2021 .SHORT TERM...(This evening through Saturday night) Issued at 140 PM MST Fri Feb 5 2021 Satellite imagery and 500mb RAP analysis early this afternoon showed northwest flow prevailing above the High Plains on the western side of a large upper trough. A disturbance was moving through the northwest flow and into the central Rockies, generating cloud cover and light snow in the mountains. At 1:00 PM MT, temperatures ranged in the 40s across our area with northwest winds turning west at 10 to 20 mph. Cloud cover began sliding into the region from the west off of the Rockies. For tonight and early Saturday, the disturbance embedded in the northwest flow aloft advances southeast towards the High Plains and produces a northwest to southeast oriented band of snow over central Nebraska and northeastern Kansas. The heart of this band will be well off to our northeast, but areas east of a line from Wray, Colorado to Gove, Kansas could get clipped by some light snow. The main timeframe to watch will be after midnight tonight into Saturday morning. At this time, the forecast calls for around one inch of snow near McCook, NE and Norton, KS with amounts quickly decreasing to the south and west. Otherwise, expect low temperatures in the upper teens to low 20s. A surface low crosses the region overnight, shifting winds to the north with the potential for gusts near 35 mph on its backside. Snow tapers off to the east Saturday morning, with breezy winds carrying on behind. Winds should go light during the afternoon hours as the low pushes further away from the region. The frigid air filtering in behind the disturbance and lingering cloud cover will make for a wide range in high temperatures and a difficult temperature forecast. Current thinking is for highs ranging from the low 20s in the northeast portion of the region to the low 40s in the southwest. On Saturday night, another round of snow looks to develop across central Nebraska as the next disturbance passes through the continued northwest flow. Again the majority of the snow will stay north of the region, but light amounts (less than a half inch) cannot be ruled out north of the Nebraska border. Temperatures fall into the single digits and teens for most of the area, with a few locations staying up in the low 20s in eastern Colorado. Will need to monitor the potential for fog development as winds turn southerly overnight. .LONG TERM...(Sunday through Thursday) Issued at 144 PM MST Fri Feb 5 2021 Much colder in the long term period with the potential for light snow as well. Sunday will be the last of the "warmer" days as the western portion of the area will see temperatures that are near the climatological average while locales further northeast will likely be cooler due to cloud cover. Another reason those locales will be cooler is that the colder air mass will move in from the Central Plains during the day which will cap highs as it moves through. It is worth noting that the upper level pattern is fairly stagnant with 500mb flow out of the northwest during most of the period as a broad trough sits across the CONUS. Snow looks to be unlikely as the surface low is currently forecasted to be too far west and south to affect the region. However, it would not be unreasonable for flurries at different points during the entire period given the colder air that is expected and potential for higher RHs aloft. Monday through Wednesday look to be fairly similar in conditions as the large scale pattern is stagnant with that upper trough across the CONUS and the arctic air mass set up over the Central Plains. High temperatures are currently forecasted to be in the 20`s during these days with lows in the single digits or just below zero. Given such cold lows, will need to watch wind chills as the forecast has them approaching negative 15 to 20 degrees F. Model guidance does hint at on and off cloud cover through these days though precip remains unlikely given the high pressure across the area. Thursday on is uncertain as guidance begins to differ on how the upper pattern will evolve starting late Wednesday. The ECMWF and GFS largely disagree on the prevailing conditions with the ECMWF bringing in moisture from aloft while the GFS is drier. Both guidance and ensembles agree that the center of the upper trough will begin to push off to the east, though both deterministic models suggest it will also dig further south. There is disagreement though on how that will happen and how far south it will dig. Either way, this will need to be watched as both NAEFS and ECMWF anomaly tables have a 2.5 percentile 850mb temperature Thursday into Friday in regards to 30 year climatology. They both also have a minimum value in comparison to 20 years of forecasts for this time period. However, this is still too far out to determine if this would happen and if it would even lead to cooler temperatures given that the area is already below average and there are hints of snow moving through. Will continue to monitor how the pattern evolves and if the suggested anomaly remains. && .AVIATION...(For the 06Z TAFS through 06Z Saturday night) Issued at 900 PM MST Fri Feb 5 2021 A stationary front bisects the KGLD and KMCK terminals late this evening with sub VFR cigs on the cold side of the front (KMCK) and VFR cigs on the west (KGLD). From taf issuance through 12z KMCK is expected to remain in sub VFR cigs with a chance for light snow. Stratus is expected to get close to KGLD but for now should be just east/northeast of the terminal. Winds at KGLD begin from the south under 10kts veering to the northwest up to 10kts by 12z while KMCK remains from the east and northeast at speeds up to 10kts. From 12z-00z winds at both terminals become north to northeasterly in the morning with gusts up to 30kts expected then shifting to the east and southeast at speeds up to 10kts in the afternoon as a cold front pushes west and strong high pressure drops into the central plains. KGLD is currently expected to remain VFR while KMCK remains under sub VFR cigs. From 00z-06z winds at KGLD increase from the south-southeast around 15kts with higher gusts, 11kts or so from the east- southeast at KMCK. Cigs are expected to lower sub VFR at KGLD toward the end of the period as stratus moves west toward the terminal. KMCK remains under sub VFR cloud cover. && .GLD WATCHES/WARNINGS/ADVISORIES... KS...NONE. CO...NONE. NE...NONE. && $$ SHORT TERM...JBH LONG TERM...KAK AVIATION...99
Area Forecast Discussion
National Weather Service Jackson MS
926 PM CST Fri Feb 5 2021 .UPDATE... Updated for evening discussion. && .DISCUSSION... The forecast thinking is generally the same with showers expected to increase later tonight and shift northward as we go through Saturday. Have just made minor adjustments to the overnight and early morning forecast to account for latest observational and near term guidance trends. /EC/ Prior discussion below: Tonight and tomorrow: Scattered showers continue south of I-20 into the evening...though should start to drift southward/have a few breaks before 05/06z when another quick disturbance will stretch that precip slightly northward again. Going into tomorrow...the rain across the region remains the main issue. HRRR was far more conservative with the northern extent of the showers. Whereas the 12Z NAM was far more aggressive with lifting that stalled front back to the north a bit... having more precip across the entire area by 12Z. The 18Z NAM came in and eliminated the pops north of I-20 before noon tomorrow, far closer to the HRRR. Trended the forecast in this direction. And although the pops may remain conservative, the increasing cloud cover in the east and north...will result in cooler highs, particularly east of I-55, by at least a couple of degrees. /HJS/ Tomorrow night through Tuesday: The forecast period starts off tomorrow night with a longwave trough draped across the CONUS with an embedded shortwave trough rounding the base of the longwave over the Lower Mississippi Valley. Surface cyclogenesis will be underway along a coastal baroclinic zone with the surface low lifting through the Florida Panhandle and along the Carolina coast by Sunday morning. Associated showers will continue along the Hwy 82 corridor through the overnight hours with dry conditions returning to the area by Sunday morning. A surface cold front over northern Arkansas and Tennessee will make little southward progression as it becomes oriented parallel to upper flow aloft. As such, no airmass change is expected with the coldest air bottled up over the Northern Plains and Midwest. Temperatures will moderate heading into the beginning of next week with afternoon highs climbing into the low to mid 60s by Monday with upper 60s to near 70 possible on Tuesday, especially south of I-20. A shortwave ejecting through northern Mexico will bring another round of rain to the area Monday night into Tuesday. Global guidance differs with respect to the strength of the wave with the ECMWF depicting a stronger wave and wetter solution while the GFS remains weaker and drier. Kept the forecast in line with the national model blend and will continue to advertise rain chances. Wednesday into next weekend: The main focus for the long term forecast period will be the potential for winter weather along with dangerously cold temperatures late next week into the weekend. Ensemble guidance continues to depict a pronounced signal for an intrusion of very cold arctic air beneath active southwesterly flow aloft. This synoptic setup, along with top analogs, supports a multi-day period of dangerous cold with several chances for winter weather. Strong cross polar flow will allow a frigid arctic airmass to spill into the Northern Plains on Wednesday. This airmass will be anomalously cold with an associated 1050mb surface high (2-2.5 sigmas above normal). Meanwhile, further aloft, persistent southwest flow will remain in place over the Lower Mississippi Valley with embedded perturbations ahead of a potent shortwave trough forecast to dive into northern Mexico by Thursday morning. The arctic cold front will move through the area during the Wednesday night to Thursday timeframe and will establish a shallow sub-freezing layer beneath warm temperatures aloft. This will set the stage for potential winter weather as aforementioned perturbations swing through aloft followed by the main shortwave trough ejection. While confidence is increasing that at least some portion of the area will see accumulating winter weather, exact timing and placement remain more uncertain and will hold off on mention in the HWO/graphics for now. Predominate precipitation type looks to be a mixed bag of rain, freezing rain, sleet and potentially some snow if enough moisture becomes juxtaposed with deeper cold air. The center of the arctic high is progged to slide into the Southern Plains and Mississippi Valley by the weekend and will usher in a dangerously cold airmass characterized by temperatures anomalies 15- 22 degrees below normal. This will yield overnight low temperatures dropping in the low 20s to teens and afternoon highs struggling to climb into the low 30s. Furthermore, wind chill values are forecast to drop into the single digits across much of the area. While the signal for dangerous cold remains strong, drastic run-to-run model variability continues to make pinpointing a focused timeframe very difficult this far out, thus will keep the HWO/graphics clear for now. It is worth noting that this potential winter weather and dangerous cold event has a high ceiling and potentially high impacts due to the combination of ice/sleet/snow followed by arctic air. However, the magnitude will be dependent on several moving parts coming together just right and exact details remain unclear at this point in time. The forecast will continue to evolve over the upcoming week and as such, the reader is strongly encouraged to stay abreast of the latest forecast throughout the week as details are ironed out and model guidance comes into better agreement. /TW/ && .AVIATION... 00Z TAF discussion: Expect rain to diminish early this evening in the Pine Belt area, but a significant trough approaching Saturday will bring moist ascent with rain and IFR ceilings redeveloping across much of the area by afternoon. Light surface winds will pick up from the east Saturday and could be gusty at times. /EC/ && .PRELIMINARY POINT TEMPS/POPS... Jackson 36 49 39 56 / 29 66 23 0 Meridian 37 47 38 54 / 28 64 26 0 Vicksburg 38 51 39 55 / 21 57 18 0 Hattiesburg 41 51 41 59 / 68 82 12 0 Natchez 40 53 40 58 / 45 79 11 0 Greenville 35 48 35 49 / 1 32 38 0 Greenwood 35 49 36 52 / 1 28 48 0 && .JAN WATCHES/WARNINGS/ADVISORIES... MS...None. LA...None. AR...None. && $$
Area Forecast Discussion...UPDATED
National Weather Service North Platte NE
852 PM CST Fri Feb 5 2021 .UPDATE... Issued at 852 PM CST Fri Feb 5 2021 A forecast update is in place for temperatures using hourly forecast temperatures derived from the short term model blend plus bias correction, the RAP model plus bias correction and the HRRR model without bias correction. This lowers highs Saturday a few degrees and attempts to capture the arctic air progressing south through nrn Nebraska this evening. The rest of the forecast is on track. The evening models appear to be tracking the highest snowfall amounts through the Sandhills as predicted. && .SHORT TERM...(This evening through Saturday night) Issued at 309 PM CST Fri Feb 5 2021 The primary forecast challenge centers on the threat for multiple rounds of accumulating snow this weekend, and temperatures through next week. Winter Weather Advisories remain in effect overnight tonight with the addition of a Winter Storm Warning for Custer County. Not much has changed with respect to the overall pattern across much of the CONUS with a large-scale trough pivoting across the northern Great Lakes and highly amplified flow upstream of this feature with a building ridge off the West Coast. Caught in between these features, the local area is seeing the influence of an upper-level jet as it slides just to the south. At the surface, the Arctic cold front bisects the area in half oriented northwest to southeast with highs only in the 20s and clouds as of 20z to the northeast with upper 30s to low 40s across the southwest. This front will continue to stall this afternoon but should see a renewed southward push as a quick diving clipper system approaches the area late this evening. As this moves south, mid-level fgen will increase quickly from 03z to 09z which will tap into PWAT values which climb to the 0.25-0.35" range. While this isn`t overly impressive, the forecast forcing for ascent is expected to be rather strong which will allow forecast QPF values to overachieve. Indeed, numerical guidance has started to hone in on a consensus that paints a stripe of liquid precipitation exceeding 0.3". This is in good alignment with the latest NAM and Canadian output, SREF/HREF probabilities, as well as latest high res guidance. While the GFS remains the furthest south with its output and therefore is considered the outlier, the ECMWF has trended upwards with its QPF output and aligns with the aforementioned list in terms of location. Greatest uncertainty with snow amounts will exist along the southern edge of the snow gradient with increasing confidence north across the Sandhills. Subsequent shifts will have to monitor closely for any southward shift towards the fairly resolute GFS output. As for snow amounts...given the magnitude of cold air in place, expecting SLR ratios to exceed climatological values and will likely climb above the 75th percentile. This puts much of the area in the 16:1 to 18:1 range with some guidance even suggesting making a run at 20:1. This is plausible given a deep DGZ and strong lift originating in this zone. Will not go this aggressive, however. Even with the lower SLR values, snow amounts should lead to widespread 2-5" total accumulations with a small area approaching 4-7" limited to Custer County. As a result, opted to continue the Winter Weather Advisory across the area with the lone change being to upgrade Custer County to Winter Storm Warning after coordination with eastern offices. Winds aren`t likely to be overly strong with this event, peaking around the 10 to 20 mph range overnight which should limit the blowing snow potential. Snow will wind down through the late morning hours as the focus shifts to the east and fgen rapidly diminishes. Morning lows Saturday will fall into the single digits to teens across the area with wind chills as cold as 5 to 15 below zero possible with the coldest values expected across far north central Nebraska. Expect a break from the snow during the bulk of the daytime on Saturday. Highs should only reach the low teens to low 30s northeast to southwest. Snow will renew late Saturday evening as a second mid- level disturbance moves overhead. Similar to the first round, forcing will largely come from increasing fgen and warm air advection. Moisture will be a little more limited and focus for this lift will be further north than the previous round. New snow accumulations will generally fall in the 2-4" range therefore will have to monitor this for additional winter weather headlines but will forego any issuance at this time to not mix messaging with the first round. Snow will linger into early Sunday morning with lows dropping a further 5 degrees across the board. Snow will diminish slowly through the day Sunday, with the last of the potential ending for areas north of Highway 92 by early evening. Can`t rule out some light snow persisting later, but confidence is low at this time. Highs Sunday will be similar to what was seen Saturday, ranging from around 10 in the northeast to around 30 in the southwest which will likely be the last day of seeing temperatures approach the freezing mark for an appreciable amount of time. .LONG TERM...(Sunday through Friday) Issued at 309 PM CST Fri Feb 5 2021 Beginning 00z Monday. The region remains entrenched in northwesterly flow for Monday through the middle part of next week. Strong surface high pressure will settle into the area from eastern Montana which will only reinforce the cold air expected to move in. Sunday night into Monday, will be watching for some light snow to develop on the leading edge of the surface high pressure system. Moisture will be fairly limited so any snow amounts are expected to remain fairly light. Daytime highs will top out in the single digits to low teens Monday through Wednesday, which is 25 to 35 degrees below normal each day. Morning lows will fall below zero across the area, even approach the negative teens. This alone is enough to cause concern for extreme cold across the area. Though no one day appears to be overly windy, any wind developing will only exacerbate the cold by introducing wind chill values falling into the -20s. At this moment, no one day appears to be overly breezy given persistent high pressure in place across the local area and eastward. In summary...while cold temperatures are confident at this time the precise wind chill values remain in flux somewhat and are lower confidence. Either way, prolonged exposure to the expected air temperatures alone will be enough to cause problems to anyone not properly prepared so plan on limiting outdoor exposure and layering up each morning through the extended period. Reinforcing cold air arrives on Thursday with the approach of another surface high in the 1035-1045 hPa range. As a result, expecting the coldest day of the week on Thursday. We could see additional light snow across our southwest zones Thursday into Friday, but differences between the main model outputs remain and ensemble guidance isn`t highlighting any one particular period as a slam dunk so will keep inherited PoPs of less than 20% as they are. && .AVIATION...(For the 00Z TAFS through 00Z Saturday evening) Issued at 534 PM CST Fri Feb 5 2021 The area of IFR/LIFR in snow and low ceilings near KIBM will move east and expand north and south across wrn Nebraska by 06z, and ncntl Nebraska by 08z. This area of snow and low ceilings/vsby will exit wrn and ncntl Nebraska by 12z Saturday. Areas of MVFR/local IFR ceilings are expected across wrn and ncntl Nebraska throughout day Saturday. && .LBF WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory until 9 AM CST /8 AM MST/ Saturday for NEZ005-008>010-023>029-035>037-057-059-094. Winter Storm Warning until 9 AM CST Saturday for NEZ038. && $$ UPDATE...CDC SHORT TERM...NMJ LONG TERM...NMJ AVIATION...CDC
Area Forecast Discussion...Updated
National Weather Service Saint Louis MO
909 PM CST Fri Feb 5 2021 .UPDATE... Issued at 900 PM CST Fri Feb 5 2021 New model data is trickling in this evening. The 00Z NAM is already out through Sunday into Monday, and it seems to compare well with the 18Z NAM for our snow tomorrow. Both runs of the NAM are drier than our going forecast, and would therefore produce less snow. All of the thermodynamic forcing still looks strong, but it`s slightly displaced from the moisture. The latest run is also a little slower bringing precipitation into our area during the afternoon, perhaps due to the very dry low levels that the snow will have to overcome. While we don`t yet have a new run of the GFS, the 18Z run was similarly slower than the current forecast, but made up for some of the slower onset of precip with more QPF on Saturday evening to yield similar snowfall amounts to our forecast. With the latest deterministic NAM showing the possibility of lesser snowfall amounts than previously expected, and no other updated guidance at the moment, I do not have high enough confidence to make changes to our current forecast and Winter Weather Advisory. Carney && .SHORT TERM... (Through Late Saturday Night) Issued at 324 PM CST Fri Feb 5 2021 Main takeaways in the short term forecast: -Snowfall totals for Saturday afternoon were increased to reflect growing confidence in higher QPF and measurable snow across the CWA. -A Winter Weather Advisory will take effect at 9am Saturday and last through 9pm Saturday for northern/central MO and west-central IL. -Behind the system, the most bitter cold we`ve seen so far this season will bring wind chill values between -5F and -10F across the CWA. A longwave trough is now squarely in place across the CONUS, which will set the stage for the cold, unsettled pattern through the forecast period. Other than a chance of light snow tonight along the I-70 corridor, which is depicted among a few of the short-range deterministic guidance and CAMs, an uneventful night is expected. Winds will stay out of the west/northwest this evening, and while the coldest temperatures stay away from the northern CWA, the entire area should end up well-below-freezing tonight. If winds were a bit more northerly, temperatures would likely sink much lower with colder air atop a snowpack north of MO being advected south. A notable difference from the previous forecast is the organization of the shortwave trough that makes it way through the CWA along the periphery of the longwave on Saturday. Previously, two areas of forcing in the northern and southern streams did not seem to phase well-enough to result in any robust snowfall. However, nearly all deterministic and ensemble guidance is now in fairly good agreement that the two maxima of PVA will be closer together and phase/amplify over MO. The latest HREF mean snowfall totals suggests a broad swath of 2-4" of across the CWA, with locally-higher amounts. Taking a closer look at the constituent members of the 12Z HREF, the HRRR seems to have influenced those significantly-inflated numbers. That being said, all guidance is trending upward in terms of QPF in conjunction with the better forcing organization. The National Blend of Models is now suggesting higher snowfall totals in the northern portion of the CWA, approaching 4" when all is said and done tomorrow night. Differing from the HREF, however, it does have lower totals (1-2") along and south of I-70. Looking closer to the surface, guidance agrees on a fairly robust axis of 850-700mb frontogenesis across the central third of Missouri. Model soundings also show a deep DGZ with at least modest lift in that layer, further solidifying the notion of not only higher snowfall totals, but periods of time where snowfall rates could reach 1" per hour. In these bands, visibility would certainly be restricted and hazardous travel would be a concern. After taking into account the consensus on higher snowfall totals, and also considering higher SLRs where temperatures aloft will be much colder, snow totals were increased to 2-4" of snow across north/central MO and west-central IL, 1-3" along I-70, and up to 2" south of that. A Winter Weather Advisory will take effect at 9am Saturday and last through 9pm Saturday for northern/central MO and west-central IL, where snow totals will be highest. I will caution that, given the trend in guidance and the potential for mesoscale banding, locally-higher amounts are possible. The truly-cold air rushes into the region associated with an arctic air mass behind this system tomorrow afternoon through tomorrow night. Not helping to moderate temperatures, winds will be more northerly tomorrow evening. As mentioned earlier, this wind direction will advect even-colder air off of the snowpack in southern Iowa into our CWA. Wind chills knock on the door of Wind Chill Advisory Criteria (-15F) in far northeast MO/west-central IL, but confidence in winds being strong enough to drop the wind chills further precluded me from issuing a product at this time. Regardless, the coldest (both in terms of true temperatures and wind chills) night of the season is expected Saturday night. MRB .LONG TERM... (Sunday through Next Friday) Issued at 324 PM CST Fri Feb 5 2021 Attention was given to the active weather in the short term, but the main points of concern through the extended period: -Well-below-average temperatures continue through the end of the period overall, but brief periods of "less-cold" air remain a possibility. -Confidence in another round of snow on Monday continues to increase across the northern half of the CWA, but timing/position uncertainties abound amidst the near-zonal mid-level flow. -A period of relatively-dry weather takes hold by mid-week, but the bitter cold remains in place. Sunday will be the first full day of the true bitter cold, and locations in northeast MO and west-central IL may break low maximum temperature records. The record "low-high" temperature at KUIN (Quincy Regional Airport) is 13F, and the latest forecast tops out just around 12F. Northerly winds will aid colder air to advect off of the snowpack to our north in addition to the cold air associated with strong surface ridging. Short term guidance and CIPS Analogs from Saint Louis University stay true to the bitter cold, as they have in the recent past. Another shortwave appears poised to translate east across the base of the longwave trough Monday. While there seems to be more agreement among deterministic and ensemble solutions than in previous forecasts, timing and position differences regarding the strongest forcing still exists. The pattern of nearly zonal flow typically results in these events that are difficult to nail down until about 48 hours prior, but the signal for precipitation is consistent from the last several guidance suites. WPC Cluster Analysis is supportive of precipitation in the northern CWA: every cluster has a swath of precipitation for Monday in that area. With attention being paid to the near-term concerns, the NBM PoPs were left in, but are likely too low. Temperatures will certainly be cold enough for snow where it precipitates, and the very cold air aloft will likely lead to higher SLRs. Right now, the best chances for snow are north of I-70, where the forcing will pass through. After Monday/Monday night, the main story remains the very cold air, but no robust signals for precipitation exist. Again, zonal flow will rarely show its hand for precipitation until the event gets closer, but there are some signals at some more amplification of the upper-level pattern that may break us free of the longwave trough late next week. While PoPs after Monday night remain low, quick rounds of precipitation are not off the table through Friday. MRB && .AVIATION... (For the 00z TAFs through 00z Saturday Evening) Issued at 544 PM CST Fri Feb 5 2021 VFR flight conditions are expected to prevail across the forecast area through Saturday morning. Some very light snow/flurries have developed over a small part of eastern Missouri, north of the St. Louis Metro area, and stretching into south central Illinois. Air near the surface is very dry, so this light precipitation may not even reach the ground. The next round of precipitation to affect the region will move in to central Missouri during the late morning or early afternoon, and spread east over the entire area by mid to late afternoon. Snow will bring MVFR ceilings and MVFR to IFR visibilities which will persist through the end of the forecast period. Carney && .LSX WATCHES/WARNINGS/ADVISORIES... MO...Winter Weather Advisory from 9 AM to 9 PM CST Saturday for Audrain MO-Boone MO-Callaway MO-Cole MO-Gasconade MO-Knox MO-Lewis MO-Lincoln MO-Marion MO-Moniteau MO-Monroe MO- Montgomery MO-Osage MO-Pike MO-Ralls MO-Shelby MO-Warren MO. IL...Winter Weather Advisory from 9 AM to 9 PM CST Saturday for Adams IL-Brown IL-Calhoun IL-Greene IL-Jersey IL-Macoupin IL- Montgomery IL-Pike IL. && $$ WFO LSX