Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 01/31/21

Area Forecast Discussion
National Weather Service La Crosse WI
556 PM CST Sat Jan 30 2021 .SHORT TERM...(Tonight and Sunday) Issued at 210 PM CST Sun Jan 30 2021 Broad thermodynamic lift (RAP 280-295 K sfcs) working on deepening low level saturation to produce areas of freezing drizzle across parts of SE MN, NE IA early this afternoon, inching toward far SW WI. The saturation will continue to deepen, gradually getting cold enough to introduce ice into the cloud this evening as responsible sfc low tracks east/northeast across the mid mississippi river valley. Some hints of a seeder-feeder potential too, which could limit the freezing drizzle in some locations. Some icing should be expected on untreated sfcs - impacting travel. Like our most recent storm system/snow maker, the main driver of the pcpn will be the thermodynamics. The parent upper level trough holds to the south without much indication of energy pivoting around the trough. Not much/if any upper level jet support. Frontogenetic aid also looks to be minimal with the RAP/NAM only hinting at some potential banding across NE IA/SW WI tonight. There is a fetch of 850 mb moisture transport fueling some of the snow tonight. How much snow? With a milder airmass in place and a DGZ under 100 mb, ratios look to be more in the 10/15:1 range. That said, deep isothermal look in the RAP soundings, roughly around -5 C, could support more dendrites. General 3 to 6" overall, with less on the fringes north of I-94 and portions of SE MN. The bulk should have fallen by day break Sunday, with potentially another 1/2 to 1 that morning. Winds will stay up a bit tonight, but don`t look high enough to move around what should be a wetter snow all that much. Don`t think drifting/blowing will be a big concern as a result - but will keep an eye on it. .LONG TERM...(Monday through Saturday) Issued at 210 PM CST Sat Jan 30 2021 Two main focuses for next week: potential mid week storm followed by cold air for the weekend. Wed-Fri Storm? Pretty consistent signal that a shortwave will drop southeast from western Canada to across the Upper Mississippi River valley Wed night/Thu. Meanwhile, shortwave in the southern branch of the upper level flow churns over the desert southwest, eventually ejecting northeast toward the region. A few ways this could go... 1) The shortwaves stay separate. In this scenario, the northern stream bit of energy would bring widespread pcpn to the region, especially for northern sections. Temps would be cooler with mostly snow favored - minor to light accumulations. The southern wave could then roll toward the local forecast area on Thu-Fri. The sfc low track would be south/east, putting parts of the area under the deformation region. Temps would support mainly snow with some accumulations 1b) There are considerable model differences in strength and timing of the southern shortwave - by as much of a day in timing. Could be a pretty good swath of snow too. 1c) Can`t rule out the southern shortwave staying south, with little to any impact locally. 2) The shortwaves merge. Not the favored solution currently, but if they would, stronger, more dynamic storm system could march through the area, bringing milder, more moist air northward to fuel the storm. A lot more rain/snow would be the result. Overall, decent confidence with the northwest shortwave and snowfall potential in the Wed time period. Southern shortwave - not so much. Higher potential impacts with the southern piece and it bears a close watch. Will let model blend dictate pcpn chances for now. Cold for next weekend? while there are disagreements in how the shortwaves move/interact for next week, the models are in decent agreement with funneling cold air southward into the region. GFS currently the more aggressive/cold, but both suggest highs in the teens and single digits above/below zero for lows. && .AVIATION...(For the 00Z TAFS through 00Z Sunday evening) Issued at 550 PM CST Sat Jan 30 2021 Precipitation slowly filling in on radar around LSE the last couple hours but drier air is leading to a slightly delayed onset for RST. Should see light freezing drizzle perhaps mixed with light snow develop at both sites around or shortly after the beginning of this TAF period. Expecting only light ice amounts, if any. This will be followed by a fairly quick transition to all snow within a few hours. MVFR ceilings and visibilities will give way to IFR conditions as the snow intensifies overnight. The snow should begin to lighten in intensity after 12Z, tapering off at RST by late morning and at LSE likely by 18Z. Snow accumulations are expected to range from 2 to 4 inches, likely toward the higher end of that range at LSE. Easterly winds this evening will hold roughly around 10 knots, perhaps with a few gusts to near 20 knots. Winds will slowly back to the north by Sunday morning, remaining around 10 knots. MVFR cigs will persist at LSE through the remainder of the period, likely IFR at RST. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...Winter Weather Advisory until 6 PM CST Sunday for WIZ032>034- 041>044-053>055. Winter Storm Warning until 6 PM CST Sunday for WIZ061. MN...Winter Weather Advisory until noon CST Sunday for MNZ079-086>088- 094>096. IA...Winter Weather Advisory until noon CST Sunday for IAZ008>011-018- 019. Winter Storm Warning until noon CST Sunday for IAZ029-030. && $$ SHORT TERM...Rieck LONG TERM....Rieck AVIATION...Kurz
Area Forecast Discussion
National Weather Service Grand Forks ND
917 PM CST Sat Jan 30 2021 .UPDATE... Issued at 917 PM CST Sat Jan 30 2021 Low level flow has shifted to the north across our CWA cutting off better low level moisture and deeper low level super-saturation, decreasing probability for additional freezing fog. Low stratus and patchy fog will continue however due to saturation within CAA behind upper trough. Most intense/organized snow showers have also decreased in intensity. There are pockets of light snow lingering, however trends are match up with idea of decreasing impacts and much less snow totals from this point forward. QPF signal for the rest of the night remains light and with a trend toward weaker synoptic ascent only a dusting of additional snowfall appears likely. I felt comfortable letting the Winter Weather Advisory expire at 9 PM, and made adjustments to match trends with light snow. Considering expansive low stratus, I`m not confident in low temperatures reaching the single digits in our northwest as some bias corrected guidance was indicating (would probably need clearing), so I adjusted lows toward 2m guidance favoring overnight/morning lows in the teens/20s. UPDATE Issued at 632 PM CST Sat Jan 30 2021 Mid level shortwave axis currently shifting eastward into our CWA, mid level lapse rates 7-7.5, and increasing deep level saturation has supported several convective snow bands/clusters that are shifting south and southeast relatively quickly. RAP is currently not showing much in the way of frontogensis, and this activity is likely more organized immediately along the leading trough axis/favorable region of deformation lowering confidence that we would see more than a localized 1" snow report. Web cams show 1 mile or less in these areas of snow, and there are reports of quick accumulations on roadways impacting travel. Ahead of this snow region, saturation is still too shallow to support snow and with east/southeast flow in place light freezing drizzle remains possible. The trough axis is shown to shift east through this evening and saturation should deepen enough to end freezing drizzle threat. I went ahead and extended the Winter Weather Advisory in time through 9 PM for impacted counties to account for these hazards, with improvement more likely at that point. && .SHORT TERM...(This evening through Sunday night) Issued at 318 PM CST Sat Jan 30 2021 Impacts this afternoon and evening remain possible across many areas, with freezing drizzle and light snow. The strongest radar returns are located along and just ahead of a surface boundary and 850 mb fGen. The surface low is pushing eastward across southern portions of Manitoba, with cooler air being ushered in aloft. As such, freezing drizzle will gradually change over to light snow through the afternoon and evening. A light glaze of ice remains possible where precipitation has yet to change over. Snowfall totals from today into this evening are expected to generally be one inch or less. Temperatures will fall through the afternoon, with lows tonight expected to fall into the single digits above zero for the Devils Lake Basin and teens to low 20s elsewhere. For tonight, Precipitation pushes east of the Red River, with light snow remaining in the forecast through early Sunday afternoon for portions of northwest Minnesota. Temperatures climb into the 20s Sunday afternoon, with cloud cover slowly clearing from west to east during the late evening. .LONG TERM...(Monday through Saturday) Issued at 318 PM CST Sat Jan 30 2021 Ridge builds into the Northern Plains during the early part of the week transitioning downstream by mid to late week. As the ridge moves out a deepening trough in the southwest sets up developing a surface low out ahead of it. The surface low pressure tracks NE into the Northern and Central Plains by middle to late week increasing chances for snow. Snow amounts, track, and strength are all uncertain. The possibility does exist that some type of impacts could be felt across portions of the Northern Plains as the surface low translates across the area. Monday - Tuesday... A ridge continues to build over the Northern Plains Monday through Tuesday, with warming temperatures to near freezing for highs. Warmer temperatures and partly cloudy skies bring chances for patchy fog at times, with slight decreases in snowpack. The warm air sticks around through Tuesday, with the ridge showing signs of weakening by Tuesday night. Surface low begins to move NE toward the Central and Northern Plains by Tuesday night into Wednesday. Wednesday and onward... A northern wave accompanied by a stronger southerly wave enter the vicinity of the plains Wednesday. How they interact with each other determine the strength of the surface low. Track of the system is uncertain, with a northerly track favoring stronger signals toward moderate snow accumulations and higher wind potential. A southerly track favors weaker forcing and little to no accumulations. Ensembles have started to cluster toward the later, with a southerly track being favored for a majority of members. The possibility is still out there for a northerly track, but is slim at this point as these remain far outliers. We would need the northerly wave and southerly component to interact with one another to favor a higher impact event. At this time that is look less likely through ensembles. The northerly wave brings decent moisture and lift toward the area, with saturation through the 500mb level. With adequate lift the potential exists for chances for snow across the Northern Plains. How impactful the system will be for the area is uncertain as the southerly wave looks to be stronger and move further south of the region. This system is of interest and will be closely monitored over the coming days. Otherwise, on the backside of the system temperatures look to drop down and become cooler by next weekend. && .AVIATION...(For the 00Z TAFS through 00Z Sunday evening) Issued at 533 PM CST Sat Jan 30 2021 Snow is spreading from northeast ND and far northwest MN south and east early in the TAF period, while patchy freezing drizzle still can`t be ruled out ahead of this area of snow through mid evening. The main system transitions east through the evening/overnight with any lingering precip ending west to east by midnight. While periods of MVFR ceilings are occurring early, there should be a trend towards IFR ceilings through the night and into Sunday morning. A west to east improving trend is expected Sunday afternoon with VFR returning in eastern ND, though IFR (or even LIFR) ceilings may linger through the afternoon in MN. && .FGF WATCHES/WARNINGS/ADVISORIES... ND...None. MN...None. $$ UPDATE...DJR SHORT TERM...Lynch LONG TERM...Spender AVIATION...DJR
Area Forecast Discussion
National Weather Service Green Bay WI
533 PM CST Sat Jan 30 2021 Updated aviation portion for 00Z TAF issuance .SYNOPSIS... Issued at 240 PM CST Sat Jan 30 2021 Snow tonight into Sunday, with the highest totals near the lake in east-central Wisconsin. Above normal temperatures will continue Sunday and through most of the upcoming work week. A very energetic and progressive pattern is expected across North America for most of the forecast period. Gradual amplification will also occur. That will result in consolidation and slowing of the progression late in the period, with a strong ridge off the West Coast and a trough somewhere downstream over western or central NOAM. The medium range models were struggling to lock onto the exact structure of the ridge, and that was resulting in considerable differences in the handling of the downstream trough. The result is a higher than normal degree of uncertainty in the forecast details during the latter part of the period. Temperatures will be considerably above normal for much of the period, then turn colder (possibly significantly so) near the end of the period. Honing in on the specifics of the precipitation events was very difficult. But given the energetic nature of the pattern it`s likely amounts will end up AOA normal. && .SHORT TERM...Tonight and Sunday Issued at 240 PM CST Sat Jan 30 2021 Focus is on fgen associated area of light snow this afternoon, followed by more widespread snow this evening into Sunday. Snowfall totals in the 24 hour period from 00Z/Sun to 00Z/Mon increased around half in inch to an inch for most locations, and a little more in Manitowoc County, but this increase did not warrant any changes to the Winter Weather Advisory. Expected snowfall amts could end up a little more than 3 inches in the Wood to Kewaunee tier of counties, but this will accumulate over a 24 hour period (as supposed to 12 hours) and Saturday night is not a high travel time. Therefore, opted to keep just the southern tier of counties in the WW.Y. Also, given that most snow events have under performed this year and there is once again a wedge of dry air to overcome first, confidence is medium on snowfall amounts overall. Surface analysis at 20Z showed the main low pressure system entering western MO. Meanwhile, ahead of this low mid level fgen forcing along with an upper level jet streak has allowed a persistent area of light snow showers to gradually move north across the CWA today. The band started in central WI this morning and as of 20Z was across northern and far NE WI. In places where the column is able to saturate and snow is reaching the ground visibilities around 1 1/2 to 2 miles are occurring for brief periods. The HRRR and NAMNest seem to have the best handle on this band of snow, and keep at least a few flurries or light snow around in the far north until the main snow meets up with this band later tonight. Snow amounts associated with this band will generally be light, with up to half an inch possible. Tonight...Sfc low tracks from central MO towards southern IL and IN. Deformation zone snow is expected to move northward into the GRB forecast area, arriving between 00Z- 06Z/Sun for most. Onset timing as been a challenge as there is some dry air filtering in on easterly winds. This could delay timing a couple hours, especially across northeast WI. The main low and associated forcing will be concentrated farther south, so snowfall rates will overall be on the light to moderate side, but fairly steady. Overnight snow totals will range from 1 to 3 inches, with slightly higher amounts in the Advisory counties. Sunday...While bulk of the snow will fall overnight, a lingering surface trough and cyclonic flow will generate another half an inch or so after sunrise Sunday morning, aside from Manitowoc and Kewaunee counties where another inch or two will be possible through Sunday. In total, 2 to 4 inches of snow is expected south of line from roughly a Wausau to Shawano, to Green Bay, to Algoma. Locally higher amounts of 5 to 6 inches will be possible in Manitowoc Co. due to E/NE winds providing some lake enhancement. Wind gusts of 20 to 30 mph will also create some patchy blowing snow and reduced visibilities at times, especially in open areas across central WI and near Lake MI. Temperatures...Readings will not fluctuate too much over the next 30 hours, with lows tonight in the 20s and highs Sunday upper 20s to around 30 degrees. .LONG TERM...Sunday Night Through Saturday Issued at 240 PM CST Sat Jan 30 2021 Deep cyclonic flow with a component off Lake Michigan supported lingering low-end PoPs and flurries into Sunday evening despite most of the models ending precipitation by then. Don`t anticipate much additional snow accumulation however. A couple days of quiet/dry weather will follow as upper riding shifts across the region. Significant changes have occurred to the forecast during the latter half of the work week. After a couple days of depicting a strong Colorado Low tracking across the Plains and into the forecast area during the latter half of the work week, the bulk of the medium range guidance has abandoned that idea. That appears to be because the energy reaching the West Coast is now forecast to split, with the northern portion being stronger and racing eastward more quickly. That would also result in less of an influx of warm air, and more likely a light snow event for the area rather than a significant mixed precipitation event which was favored by the Colorado Low scenario. Hopefully the guidance will begin to settle down during the next couple days. For now, simply backed away from the mention of a strong storm we`d been carrying in the HWO. Most of the medium range guidance favors temperatures dropping below normal at the end of the forecast period and beyond. But that`s been forecast in those time ranges a few times earlier this winter and it hasn`t really happened yet. Luckily, what would be the core of the cold outbreak is still beyond the end of the forecast period so there is time before we need to forecast specific temperatures for it. && .AVIATION...for 00Z TAF Issuance Issued at 532 PM CST Sat Jan 30 2021 A combination of MVFR and VFR cigs to persist through the evening as snow slowly works its way up from the south. The main snow event will arrive late this evening and persist through the rest of the TAF period. As the snow spreads in from south to north expect MVFR to occasional IFR cigs, and IFR to possible LIFR vsbys within the heaviest snow bands. Timing in TAFs reflects the latest trends, but with some dry air to overcome at the onset, snow timing could be pushed back a couple hours. Snow will taper off Sunday afternoon as conditions improve across the region. && .GRB WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory until 3 PM CST Sunday for WIZ045-048>050. && $$ SYNOPSIS.......Skowronski SHORT TERM.....KLJ LONG TERM......Skowronski AVIATION.......Kurimski
Area Forecast Discussion
National Weather Service Memphis TN
927 PM CST Sat Jan 30 2021 .UPDATE... Forecast remains on track. Showers will continue for the next few hours across the forecast area. Rain should come to an end in most places soon after midnight. Winds should also begin to relax as the Wind Advisory will be allowed to expire at 11 PM. Made a few adjustments to the forecast to reflect current trends. && .PREV DISCUSSION... /issued 546 PM CST Sat Jan 30 2021/ UPDATE... See aviation discussion. PREV DISCUSSION... /issued 325 PM CST Sat Jan 30 2021/ DISCUSSION... Midafternoon GOES water imagery showed a deep, compact negatively- tilted upper low centered between Fayetteville, AR and Springfield MO, lifting east. Numerous showers had developed downstream of the upper low over east AR, aided by low level warm advection and strongly diffluent flow aloft. With modest elevated MUCAPE around 200 J/KG, expect a few lightning strikes nearer to the upper low center through midevening, but severe storms are not expected. Main short term concern remains wind. NAM depicted and 925mb / 2000ft AGL winds in excess of 50 KT this evening, around the southeast perimeter of the upper low. Latest HRRR runs depicted surface gust potential of 40 knots over north MS and southwest TN through 05Z / 11 PM CST. Confidence is marginal at however, given the lack a strong isentropic downglide signature near the leading edge of the dry slot, that could help bring these stronger winds to the surface. The low level inversion may be reinforced by rain this evening to make this mixing to the surface less likely. Evening shift will reevaluate the wind advisory. The upper low will track through the Ohio River valley on Sunday, and reach the mid-Atlantic seaboard by Monday evening. Models have been consistent in depicting a shortwave lobe dropping southeast down the backside of the upper low into AL/northwest GA Sunday evening. Moisture will be limited, particularly above the -10C isotherm. GFS and ECMWF models both depict some stratospheric vorticity down to 850 mb, which may aid in squeezing out a few show showers Sunday night near the TN River. For Tuesday and Wednesday, an upper ridge over the plains will move into the MS River valley, deamplifying in the process. Southerly return flow will bring mild temps on Wednesday. Forecast confidence begins to fade a bit toward late next week, as models continue to show differing solutions to the split flow pattern. Uncertainties rest more with precipitation timing, rather than with whether late week precip will occur or not. NBM guidance appeared closest to the operational ECMWF, which itself appeared to be a good compromise between its internal ensembles, as well as the operational Canadian and GFS models. With that said, some light wintry mix could mix in during the morning periods late next week, mainly north of I-40. PWB AVIATION... Winds will remain elevated through the early evening hours. Winds will mainly be from the south. LLWS will still be an issue early in the TAF period. Winds will shift to the southwest overnight and gusts will go down. Winds will gust again tomorrow. Otherwise, showers will continue through the overnight hours into tomorrow evening. && .MEG WATCHES/WARNINGS/ADVISORIES... AR...None. MO...None. MS...Wind Advisory until 11 PM CST this evening for Alcorn-Benton MS- Calhoun-Chickasaw-Coahoma-DeSoto-Itawamba-Lafayette-Lee MS- Marshall-Monroe-Panola-Pontotoc-Prentiss-Quitman- Tallahatchie-Tate-Tippah-Tishomingo-Tunica-Union-Yalobusha. TN...Wind Advisory until 11 PM CST this evening for Benton TN-Carroll- Chester-Decatur-Fayette-Hardeman-Hardin-Haywood-Henderson- Madison-McNairy-Shelby-Tipton. && $$
Area Forecast Discussion
National Weather Service Paducah KY
550 PM CST Sat Jan 30 2021 .UPDATE... Issued at 550 PM CST Sat Jan 30 2021 Updated the aviation section for the 00Z TAF issuance. && .SHORT TERM...(Tonight through Monday night) Issued at 324 PM CST Sat Jan 30 2021 Light rain will continue across the region through sunset. There are a few lightning strikes over southwest Missouri and northeast Oklahoma near the cold front where there has been some sunshine and some dewpoints over 50F. This activity will struggle to survive in a more harsh environment over our region this evening, as evidenced by the barely there MUCAPES in the 12Z guidance. However, the HRRR has been consistently developing a linear feature along the TN border in the late evening and SPC has maintained the general thunder area over most of our region, so will continue to mention, mainly over the southwest half of the region this evening. The main area of showers is expected to push through the area this evening, and should be east of the region by 12Z Sunday. However, there is a strengthening signal for more rain/showers to slip southward in the wake of the surface low Sunday afternoon and night. This occurs as a strong disturbance develops southward on the back side of the main storm system. There is some sign of a weak surface trough sliding southward and most of the precipitation is associated with that feature. Ran with the ConsShort PoPs which will result in likely PoPs sliding south through the EVV Tri State in the afternoon and evening. There is some potential for them to continue over the Pennyrile into the overnight hours Sunday night and possibly into Monday morning. A change over to snow will be possible by late Sunday evening, but surface temperatures will struggle to get to freezing, so this looks like another low to no impact event. The surface low will move eastward just to the north of I-64 tonight. Healthy southeast winds this afternoon will veer to south and eventually southwest as the low passes tonight. Winds will shift to west or northwest in the wake of the low Sunday and continue through Monday. With a stable boundary layer, mixing will be difficult to achieve tonight, so gustiness may be limited. The only sign of gustiness in the guidance is a big one, though, with the 12Z EC Ensemble probability of greater than 34kts being pegged at 90+% near the TN border. Will keep an eye on things but for now will not address the gust potential anywhere but here. Mixing will develop Sunday and northwest winds could gust over 30 mph throughout the region with the strongest winds expected over southern Illinois. Still do not have anything close enough to Advisory levels to warrant a mention in the HWO. Continued to run with the NBM for temperatures through the short term forecast period. Temperatures will climb into the 50s over the southern half of the area this evening as winds veer to south. On Sunday, blustery conditions are expected with temperatures slowly falling through 40s and into the 30s in some places. .LONG TERM...(Tuesday through Saturday) Issued at 324 PM CST Sat Jan 30 2021 Main period of precipitation chances still remain from late Wednesday night through Saturday. Although the Canadian guidance was preferred for initialization, the timing of the passage of systems through the WFO PAH forecast area late next week appeared too fast. Although it seems unlikely that there will be prolonged wet period for late next week, the Canadian and North American Ensemble guidance does hint a a wetter solution with respect to precipitable water, 850 mb moisture advection, and faster 850/200 mb winds, especially over southeast Missouri Thursday into Friday. There still remains to uncertainty and low clustering of ensemble solutions for the late week precipitation events. For that reason, leaned closest to the existing NBM initialization for PoPs, QPF, and temperatures. Temperatures may be cold enough late Thursday into Saturday for some snowfall, mainly over southeast MO foothills and southern Illinois. However, giving the widely varying solutions, will only suggest that a wintry mix may cause some potential travel concerns Friday or Saturday. Overall QPF prior to and including the wintry precipitation time period remains quite low, generally an inch or less. && .AVIATION... Issued at 550 PM CST Sat Jan 30 2021 IFR cigs to the west of KMVN/KCGI will move into the region this evening as rain continues. A few thunderstorms cannot be ruled out across the Quad State but chances are low enough that they will remain left out of the TAF. KCGI/KPAH cigs should rise to MVFR for the latter overnight hours through tomorrow while the northern terminals will struggle to get out of IFR. Rain will diminish after midnight though the northern sites will see scattered wrap-around showers through the remainder of the TAF period. Heavier rain will drop vsbys to MVFR or briefly IFR. Winds out of the southeast will shift towards southerly overnight and eventually WNW tomorrow. Winds will be gusty throughout with sustained winds of 15 kts and gusts to 25 kts this evening and during the day tomorrow with winds a little lighter in between. && .PAH WATCHES/WARNINGS/ADVISORIES... IL...None. MO...None. IN...None. KY...None. && $$ UPDATE...ATL SHORT TERM...DRS LONG TERM...Smith AVIATION...ATL
Area Forecast Discussion
National Weather Service Pocatello ID
143 PM MST Sat Jan 30 2021 .SHORT TERM...Tonight through Monday night. Early afternoon satellite and radar imagery continued to show a band of snow showers in the Rexburg-Island Park-Driggs region slowly dissipating. Looking further upstream, a broad upper low was rotating across the NE Pacific toward the NW coastal waters. Numerical models show some lingering snow showers across the Upper Snake Highlands early this evening followed by partial clearing overnight as a high pressure ridge builds across the region ahead of the approaching low. Residual low level moisture and colder overnight lows Sunday morning will help to encourage low clouds and freezing fog. The ridge axis shifts east of the divide Monday but appears to hold firm as the aforementioned low churns off the NW coast. The operational models (GFS and NAM) don`t show any intrusion of moisture into Idaho until late Monday night/Tuesday morning which continues the slower trend seen in the models over the last several runs. Temperatures run near normal through the forecast period. Huston .LONG TERM...Tuesday through next Saturday. An active wx pattern continues, with 2 storm systems of interest in the long-term period of mid-week through next weekend. Tue AM, an atmospheric river (weakening per GEFS integrated water vapor transport) will continue along the Pac Coast south of an approaching trough, with deep SW flow/warm aid advection into SE ID driving high temps into the 40s at lower elevations. The trough is forecast to split, with a positively-tilted srn branch approaching CA and closing off a sfc low, while a displaced, negative/neutral- tilted nrn branch ejects east across the nrn Rockies/srn Canada as an open shortwave. This nrn shortwave is on tap for us, bringing rain/snow showers starting Tue eve. While the SW flow will initially manifest as a S/SE sfc flow, winds quickly shift to W/SW shortly after precip begins Tue night, so we are NOT expecting another upslope-enhanced snowfall event into the srn Central Mntns. The most widespread rain/snow should fall Tue night/Wed AM, followed by a cold front Wed afternoon holding highs largely in the 30s. (This will also be our transition point to a cool/moist NW flow regime for the rest of the week/weekend.) Agreement is reasonable across the 12z GFS/ECMWF/Canadian deterministic suite including the split, trough axis progression/frontal timing, and period of heaviest precip, and this translated well into the calibrated WPC QPF guidance which we used verbatim, yielding 1-5" of snow across most of our mntn zones, and an inch or less for the Snake Plain/ern Magic Valley where temps will support rain gradually mixing with/changing to snow. Our forecast sits comfortably just above the NBM 50th percentile, and even the 90th percentile barely reaches 1" in the Snake Plain/srn highland valleys, likely due to those warm temps. Now, what could go wrong? WPC 500mb cluster analysis interestingly reveals that 45% of the ensemble members (GFS-heavy) support an alternate scenario, maintaining more of a consolidated/open trough instead of a split. These open trough-supporting clusters are all wetter than the split-supporting ensemble mean, AND slightly colder as well. SO, if our forecast above were to trend anywhere, a trend toward modestly more snowfall would seem likely. (There really are 2 moving parts here...the primary splitting solution vs. the alternate open trough/wetter solution, but also this alternate solution would REALLY need to verify the suggested colder temps to support much higher accums, esp at lower elevations.) These two potential solutions are clearly seen in the individual ensemble members at point locations as well, with strong bimodal clustering. For example, about half of the members at Pocatello come in at 1" or less, and the other half at 2-4". Similar signals are seen for other points, again with the GFS wetter than the EC. Stay tuned! Thurs, that cool/moist NW flow active storm track takes over as SE ID is sandwiched between a ridge over the Pacific and longwave troughing over the cntrl/ern US. A shortwave riding this flow is forecast to drop SE across the area Thurs eve-Fri. At this time it looks pretty progressive with light QPF amounts/breezy conditions, and a cold front Fri turning winds into the N/NW throughout the column. Thus, we should trend colder into the weekend, with perhaps another system Sun or Mon. Indeed, the 6-10/8-14 day CPC outlooks favor colder/wetter than normal conditions continuing. - KSmith && .AVIATION...Our long-duration storm system is departing SE Idaho as satellite tracks the back edge of mid/high clouds pushing east of KPIH/KIDA. Light snow continues at KDIJ, and high-res models maintain activity til 20-23z (1-4 PM). Based on radar trends, backed off to VCSH after 21z (2 PM) in the TAF and allowed cigs/vsbys to go VFR, but KDIJ is famous for stubbornly holding on to clouds/precip there over the valley...will monitor for needed AMDs. Higher confidence in shutting down by 01-02z (6-7 PM) at the very latest. Some (generally) few/sct mid-level clouds will linger elsewhere behind the departing system for the rest of the day (some of that anchored on terrain features), but aside from KDIJ -SN, wind at KBYI/KPIH/KIDA should be the only impact for aviation. MOS guidance carries a nice consistent signal that matches current obs, supporting a SW 17G27KT flow at KPIH/KIDA (lining up nicely with the major runways so low crosswind concerns) through 01-02z (lighter/more westerly at KBYI), then we relax for the night. Speaking of tonight, VFR cigs/vsbys should dominate, but confidence remains low on whether fog/low stratus will impact KIDA. This idea (already carried in the previous TAF) remains supported by NAM guidance, while the HRRR is VERY limited with development (mostly north of KIDA), the HREF ensemble mean/NBM are more widespread with low stratus but with KIDA near the srn periphery, and the GFS is mostly clear. All considered, we did not have enough confidence to sound the all-clear, so leaned on the more calibrated HREF/NBM and only nudged OVC005 to BKN005 after 07z (midnight still looks like good timing) and added VCFG (which might actually be favored if we lean toward less clouds). Maintained an MVFR deck at KDIJ overnight as well, and confidence is low there on whether this could go lower. Sun, expect a return to VFR at all terminals by late AM with perhaps some high-level clouds streaming in ahead of our next system. Precip looks to hold off until Tue though. - KSmith && .PIH WATCHES/WARNINGS/ADVISORIES...None. && $$
National Weather Service Raleigh NC
1048 PM EST Sat Jan 30 2021 .SYNOPSIS... A storm system will approach from the west tonight, and affect the region through Sunday. The upper level low pressure will then arrive from the Midwest Sunday night and Monday. && .NEAR TERM /THROUGH SUNDAY/... As of 1048 PM Saturday... Update. Winter Weather Advisory area. The initial WAA band is moving ENE across north-central NC at the moment. Thus far, only trace amounts of snow and some ice pellets have been reported. Only a few hundredths (up to 0.04) of liquid equivalent has been reported in the Triad (Greensboro and Winston- Salem). The light precipitation has only lasted about an hour or so at any given location. Some light snow has been reported as far south as Albemarle, Lexington, and Pinehurst (with some light sleet mixed at those more southern locations as well). No slick spots have been reported as of 1030 PM. The surface temperatures have dipped into the 32-33 range in the Triad, with a 8-9 degree fall in less than 2 hours with the light snow. However, we are close to nearly saturating the near surface layer with the potential for additional evaporation cooling now becoming more and more limited. The CAD high is slowly moving out, thus the dry and cold air that is currently over the Piedmont Damming region is all that is going to be advected in. Now, warming aloft will continue with the temperatures at H825 expected to soar into the 40s to near 50 with a SW wind to 45kt later tonight. Similar conditions are currently observed upstream over Tennessee where the main shield of precipitation is rapidly moving toward western NC. Partials and the latest data analysis suggest that the warm nose aloft will begin to overwhelm the column as such that the main p- type as this next round arrives will be freezing rain/rain. If the precip arrives a bit more quickly - there is still a chance of a period of additional snow/sleet before the warmth aloft completely arrives by 5-7 am. This would be most likely around the NW-N part of the Triad to near Roxboro. Otherwise, given the extent of the warm nose aloft later tonight and Sunday morning, the freezing rain that will be developing later tonight will be accruing in a very marginal situation in which the near surface layer will be around 32 or 31 for a few hours between 09z and 13z, then slowly rise into the mid 30s for most locations by noon. There is still a good chance (50/50) of 0.1 to 0.15 or so of freezing rain accrual centered in the heart of the CAD (Roxboro to Winston-Salem). However, the rainfall rates will increase around and after daybreak for a few hours. This will simply enhance the self limiting freezing rain accrual process with rates too heavy and temperatures so marginally cold enough (31 or 32) to allow accrual. Then, with the onset of daylight (solar insolation) and modifying temps to 33 or 34, all rain will end the even by mid to late morning from S to N as the wet bulb 32 or lower (line) shifts into southern VA. East and south of the Winter Weather Advisory - outside a brief period of light snow/sleet/rain as this initial band exits shortly - a cold rain is favored with slowly moderating temperatures Sunday. As of 700 PM Saturday... Update. Band of light snow heading into the western part of the Triad, including Winston-Salem and Lexington before 800 PM. We are closely monitoring the band of WAA precipitation that is currently moving ENE across the Mountains and into the Foothills and western Piedmont. Thus far, the band has produced a period of around 0.10 of precipitation in 1 to 1.5 hours time. Asheville had a period of moderate snow with visibilities of 1/2 to 3/4 mile for about an hour. This allowed a coating on the ground. The snow has reached out of the Blue Ridge into the Wilkesboro, Morganton, and Hickory areas in the past hour, where all locations are reporting moderate snow with visibilities near 1/2 mile. The transition line to sleet is as far south as Charlotte, with rain reported just to the south of Charlotte. The line will be moving quickly ENE into the Triad shortly. Thus far, it appears that the band has not weakened as the HRRR indicates as it moves through the Triad. Unless it weakens shortly, it appears that quick dusting to an inch of snow appears likely for much of Davidson, Forsyth, Guilford, and Randolph counties in the next couple of hours. The freezing level is nearly at the surface all the way to Albemarle and Troy, thus some light snow/sleet can be expected there, as well. The temperatures were in the upper 30s at 700 PM. However, the wet bulb readings were in the upper 20s. Therefore, just as what has occurred at Asheville, Hickory, Morganton, Boone, etc... readings will crash 5-10 degrees in an hour with the snowfall if the current rates within the band hold as it moves through. This would quickly coat some of the area bridges and overpasses with some slick spots. Previous discussion issued as of 305 PM Saturday... ...Winter Weather Advisory for the northern Piedmont and northern coastal Plain Counties beginning at 7 PM this evening... ...Expect to See The Greatest Impacts from Ice and Snow along and north of I-85... The overall system remains the same with the upper low lifting from the southern Plains, northeast and into the OH Valley tonight. The surface high will continue to shift northeast tonight as a warm front lifts northward into the area. Some of the remnant ridge will linger over the area slowing/limiting the northward progression of the warm front as the surface low moves into the TN/OH Valley region. Model solutions continue to generate a quick band of precipitation lifting from the southern Piedmont through the northern Piedmont and Coastal Plain this evening/early tonight as the warm air lifts over the cold air at the surface. This band will be the primary chance for snow with the system, with up to about an inch across the far northern Piedmont, while the Sandhills and southern/central Coastal Plain remaining mostly rain (though some snow could briefly mix in). In the wake of the initial band, expect a lull in precipitation activity before the next round of precipitation moves in from the west (early Sunday morning). Temperatures overnight will bottom out in the low to mid 30s, lowest north, highest south. Precipitation early Sunday morning will be variable, with snow, sleet, freezing rain and rain all possible through daybreak (mainly north of US-1). Primary p-types will be rain (south and east) or snow transitioning to freezing rain (north and west), and some sleet briefly mixing in. The upper trough will amplify west of the mountains through the day as the low drift southeast through the OH Valley. The CAD wedge will be in place Sunday over the northwest Piedmont as the warm front continues to lift through central NC. The Coastal Plain should be in the warm sector by Sunday evening. The primary surface low will sit over the OH Valley as a secondary low develops along the Southeast. Expect precipitation to persist through the day Sunday, with rain south of the warm front and freezing rain to the north. The freezing rain/rain line will retreat northward with the front through the day, lingering across the northern Piedmont into the afternoon and early evening where any lingering CAD remains. Ice accumulations will depend on the duration and intensity, but for now expect 1 to 2 tenths of an inch along the NC/VA border, tapering down to zero/trace amounts along roughly the I-85 corridor (generally north of the Triangle and Rocky Mount areas). High temperatures will vary greatly, ranging from low/mid 30s NW to mid/upper 50s SE. Impacts will depend on the ice accumulation and how much we are able to warm (melt) during the aft/eve. See Short Term discussion for impacts Sunday night. && .SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/... As of 415 PM Sunday... A mid/upr-level low will wobble from the OH Valley ewd across the cntl Appalachians and middle Atlantic this period; and that will contribute to deepening of a secondary/coastal surface cyclone up the middle Atlantic coast, while the initial surface low occludes and dissipates beneath the mid level low. The deepening and passage of that coastal low will result in weak CAA and temperatures dipping back down to around freezing over the nrn Piedmont Sunday night, ranging through the mid-upr 30s elsewhere. And while the main precipitation band/rain will be moving east and out of the cntl NC early Sunday night, continued low level saturation in cold air damming will favor periods of drizzle, or freezing drizzle over the nrn Piedmont. QPF during that time is expected to be just a Trace or hundredth, so any additional ice accrual would be a glaze at best. As the center of the mid/upr low and cold temperatures/steep lapse rates aloft wobble overhead during the day Mon, scattered showers are expected to redevelop across cntl NC through the afternoon, then gradually diminish and move ewd with the passage of the trough aloft Mon night. The heavier showers may mix with snow --similar to the mid/upr low passage on Jan 16-- but with no accumulation expected at this time. It will otherwise remain cool and mostly cloudy Mon, with temperatures rising into the upr 30s-lwr 40s - locally several degrees cooler beneath showers. Continued cyclonic flow aloft even behind the trough axis will likely maintain variably cloudy conditions through Tue morning, which along with a steady nnwly breeze, will keep temperatures overnight mostly in the low-mid 30s, with some upr 20s by morning. && .LONG TERM /TUESDAY THROUGH SATURDAY/... As of 420 PM Saturday... The mid/upr low initially along the middle Atlantic coast will lift slowly newd and allow for shortwave ridging to expand from the Plains to the middle Atlantic mid to late week. After a cool and continued variably cloudy Tue, and clearing and cold Tue night, clear and moderating conditions will follow, with high temperatures likely in the 50s-60s by Fri. The next chance of rain will also arrive late in the week, as the next trough aloft and frontal system arrive from the west Fri-Sat. && .AVIATION /00Z SUNDAY THROUGH THURSDAY/... As of 700 PM Saturday... Initial wave of precipitation between 00-04Z should be cold enough to warrant a brief period of light snow across the Triad and a rain/snow mix at RDU/RWI. Introduced a TEMPO period to cover this short duration. Otherwise, ceilings/visibilities will trend to MVFR and become IFR between 11 and 13Z, perhaps LIFR over the Triad through the end of the TAF period. Given the lingering cold air damming scenario, main precipitation shield over the Triad should be FZRA, perhaps lingering through 18Z. A brief period of FZRA is likely at RDU, but temperatures should rise for this to change over to rain by 13-14Z. All rain is anticipated at FAY. Surface winds are light to start the period, becoming east-northeast. Low-level wind shear is expected and was introduced to account for a strong low- level jet from the south-southeast at 40 knots atop the stable surface layer. Beyond 00Z Monday: Continued IFR to occasionally LIFR ceilings/visibilities are expected Sunday night and early Monday. The main precipitation shield is expected to move out around 00Z Monday, but some lingering freezing drizzle is possible over the Triad. Sub- VFR ceilings with possible rain or snow showers are again possible on Monday, along with breezy northwest winds. VFR should return Tuesday and continue through at least Thursday. && .RAH WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory from 7 PM this evening to noon EST Sunday for NCZ010-011-026>028-038>041. Winter Weather Advisory from 7 PM this evening to 4 PM EST Sunday for NCZ007>009-021>025. && $$ SYNOPSIS...Badgett/KC NEAR TERM...Badgett/KC SHORT TERM...MWS LONG TERM...MWS AVIATION...Badgett/Kren