Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 01/09/21

Area Forecast Discussion
National Weather Service La Crosse WI
947 PM CST Fri Jan 8 2021 .SHORT TERM...(This evening through Tonight) Issued at 229 PM CST Fri Jan 8 2021 Low clouds have remained locked over the area today, with no improvement expected overnight. Given a solid stratus deck, lows will likely be held up in the upper teens to 20s, though potential is there to quickly drop into the low teens if any gaps form. 08.12Z HREF suggests dense fog potential is mainly north and west of the area tonight where visibilities are already reduced and models suggest a little better cooling, but will have to watch along our northwest border from portions of southeast Minnesota into north- central Wisconsin in case this fog area ends up shifted a bit east (the 08.18Z RAP and HRRR are most bullish with this scenario). With temperatures near the top of the cloud layer hovering around -10C, would not be totally surprised if a few flurries were squeezed out as well. .LONG TERM...(Saturday through Friday) Issued at 229 PM CST Fri Jan 8 2021 Things are still looking fairly quiet into mid-week, with mild and predominately dry weather. Saturday looks very similar to today, with high pressure anchored just west and weak flow aloft. Unfortunately, this likely means gloomy low clouds and haze/patchy fog again, though some of the guidance does try to break things apart a bit by afternoon and provide some glimpses of sunshine. Not quite ready to buy into that sunnier outlook, however. Highs top out in the 20s to near 30. A little change occurs Sunday, as a shortwave pushes through the area. With a dry atmosphere, this doesn`t look promising for precipitation, but 08.12Z NAM/GFS soundings do very briefly approach saturation, so couldn`t rule out some flurries. In addition, with weak WAA/lift ahead of this late Saturday night/early Sunday morning, might have to watch for patchy freezing drizzle given moist low-levels. Confidence is low in this occurring, however. A couple of shortwaves push through the upper Midwest for the beginning of the week, but the story is similar with a dry atmosphere and not much potential for precipitation - maybe occasional flurries or a light snow shower if forcing can briefly overcome this dry air (a big "if"). 08.12Z GEFS plumes accumulated QPF does not exceed 0.08" through Tuesday for any points in our area and none of that cumulative total occurs in one go - pretty impressive agreement for little in the way of precipitation. Cloud forecasts are always tricky, and it remains to be seen whether any of these shortwaves disturb the atmosphere enough to kick the low clouds out. GEFS/EPS ensemble members show a better signal for light precipitation toward the end of next week, as the split-flow pattern finally breaks down a bit with larger-scale troughing across the Midwest. However, given large differences in timing and placement, have kept the drier NBM PoPs for now. Highs generally range from the 20s to 30s in the extended, but could warm to the mid and upper 30s by the middle of next week ahead of the potential late week system. && .AVIATION...(For the 06Z TAFS through 06Z Saturday night) Issued at 947 PM CST Fri Jan 8 2021 Generally expect LIFR to MVFR stratus across the region through the TAF period. A few larger holes in the stratus were found over northeast MN and central WI, but confidence in clearing impacting KLSE/KRST is low. While IFR vsbys couldn`t be ruled out at KRST early Saturday morning, current thinking is that highest chances will be farther west. Some modest diurnal improvement in ceilings is likely, but maintained IFR/MVFR ceilings through the day. Light NW winds expected through the period. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...None. MN...None. IA...None. && $$ SHORT TERM...Lee LONG TERM...Lee AVIATION...JM
Area Forecast Discussion
National Weather Service Denver/Boulder CO
811 PM MST Fri Jan 8 2021 .UPDATE... Issued at 811 PM MST Fri Jan 8 2021 The upper level trough that will bring snow to the area Saturday is dropping southeast across northern Nevada. Clouds will increase overnight with overcast skies for Saturday. Limited forcing from the system will keep snowfall amounts on the light side. No big changes from the 00Z NAM and HRRR models. The NAM has trended a little higher with snowfall amounts (up to an inch more), but the HRRR is a little lower. With this said, will not make any changes to the forecast at this time. Still expect the upcoming system to bring most locations an inch or 2 of snow. && .SHORT TERM...(This evening through Saturday) Issued at 238 PM MST Fri Jan 8 2021 The trough just onshore will drop southeast, bringing a weak closed low across southwestern Colorado on Saturday. This will bring a period of lift across the state, but the strongest lift will be across the south and west, and the forcing will be quite weak north and east of Denver. In addition, there`s not much moisture around. The lift will gradually saturate the atmosphere over and just east of the mountains, but developing east winds will keep a layer of drier air near the surface out toward the eastern border. Lower elevations west of the divide may have a similar situation with local downsloping. In any event, winds will be light with little orographic snow. The one exception will be in the Front Range foothills especially from about I-70 southward and possibly Monument Hill where there will be some weak upslope into a shallow slightly unstable layer Saturday afternoon. These areas could pick up 2-4 inches of snow, while elsewhere we`ll have to rely on the weak synoptic scale processes for generally an inch or two and even less as you go north and east. We did speed up the timing a little bit in accordance with model guidance which has enough low level convergence on the plains during the day Saturday to speed things along. We expect areas of light snow to develop during the middle of the day, though if there`s a more significant period it should be more like late afternoon/early evening. Current forecast and model guidance is all good for the rest, with highs around freezing on the plains Saturday and light winds. .LONG TERM...(Saturday night through Friday) Issued at 238 PM MST Fri Jan 8 2021 Not much to talk about for the extended. Departing storm Saturday night finishes up with its snowfall by sunrise Sunday, then dry. Slim chances for snow in the north central mountains toward the end of the period Thursday. Extended period picks up with the center of the 500 mb low over NW New Mexico, with trough axis pointed northeast across eastern Colorado into the northern plains. Trough continues to move slowly east with sharpening ridge over the west. As upper low departs QG ascent, what little clips the BOU forecast area, pulls away. Best moisture limited to below 600 mb, with saturated layer present in the -12 to -18c dendrite snow growth layer between 600-700 mb from about 00z-04z, then moisture tapers off after 06z. Model soundings show weak ascent continues until about the same time. Combination of weak QG ascent with weak upslope low level flow through 06z argue for likely to definite pops in the 00z-06z timeframe. Best time for snow centered around 00z Saturday. With the passage of the upper trough high pressure begins to build on Sunday and remains in place for much of the next week. Temperatures will see a warming trend, with highs in the 40s on the plains and 30s higher elevation communities Monday, warming to the 50s plains and 30s & 40s in the mountains by Wednesday. Thursday a weak trough in the upper level northwest flow dives southeast across mainly northeast Colorado. Some good jet dynamics with this one, with the nose of a 150 kt 300 mb jet taking aim over the northeast. Push of northerly wind at the surface will cool temperatures on the plains a few degrees from warm highs earlier in the week. Little moisture to work with however, and little to no pops. Only exception is slight chance pops in the northern mountains highest elevations, where upslope flow will wring out any available moisture. Possibility that the strong winds on the plains Thursday could elevate fire weather concerns with warm temperatures and strong winds. && .AVIATION...(For the 06Z TAFS through 06Z Saturday night) Issued at 811 PM MST Fri Jan 8 2021 Clouds will increase and lower through the night as a Pacific storm system approaches the region. Ceilings are expected to fall below 6000 feet after 09Z Saturday. Clouds continue to lower Saturday morning with ceilings of 500 to 2000 feet expected after 15Z Saturday. These low clouds will continue through Saturday night. Light snow is expected, mainly after 20Z. Forecast total snow accumulations for the Denver area for Saturday and Saturday evening are 1 to 2 inches. && .BOU WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...Meier SHORT TERM...Gimmestad LONG TERM...Hanson AVIATION...Meier
Area Forecast Discussion
National Weather Service Grand Rapids MI
748 PM EST Fri Jan 8 2021 LATEST UPDATE... Update .SYNOPSIS... Issued at 324 PM EST Fri Jan 8 2021 - Chilly night - Fairly quiet weather for a while - Possible trend back toward cool/snow late next week && .UPDATE... Issued at 746 PM EST Fri Jan 8 2021 The skies have cleared out around AMN where the current temperature was already lower than the forecasted min temperature. The clearing line was shifting steadily south...although it has slowed down somewhat. Either way we have updated the temperature and cloud forecast to reflect the current trends. && .DISCUSSION...(This evening through next Friday) Issued at 324 PM EST Fri Jan 8 2021 -- Chilly night -- Satellite images show clouds gradually thinning and evaporating over much of the lower peninsula from low-level subsidence this afternoon. If this clearing holds through tonight, a relatively cold night is setting up, in line with what ECMWF ensembles and other guidance have been advertising for a few days now. There may be quite a range in low temperatures depending on local conditions: duration of clear skies, pockets where winds go calm, terrain where cold air tends to drain into low areas. Overall, seems likely for a lot of single digits and teens for low temperatures. Leota (Clare County) last night stayed clear and their lows fell to 0. Can`t rule out some areas of freezing fog, particularly in northern portions of Central Michigan. -- Fairly quiet weather for a while -- Two weak shortwave upper level troughs move through over the next several days, one Saturday night into Sunday and another Monday night into Tuesday. These don`t look like they will be able to do much, as mid-levels will still be very dry. The boundary layer capping inversion heights may rise slightly as these waves pass through, but should remain below 5000 feet. Any clouds below this inversion probably won`t get any colder than -10 C, which is borderline for glaciation. Mesoscale models are showing a mid-lake convergence band over Lake Michigan on Saturday amid northeast flow from Lower Michigan and northwest flow from Wisconsin. As northwest flow becomes more dominant Saturday night, any lake effect clouds and snow present within this convergence band may reach the lakeshore counties at some point Saturday night. Even HRRR soundings in proximity to the convergence band show the convective boundary layer capped at 5000 feet and -10 C, so some light snow showers are possible but it`s difficult to envision any impacts from this. -- Possible trend back toward cool/snow late next week -- Ensemble guidance is still not fully on board with the magnitude or timing of the change in pattern late next week, but some colder air and chances of snow may arrive in the Midwest as early as Thursday night or Friday. Ensemble spread in temperature solutions going into the weekend and the following week is quite high, with the GEFS looking colder on average than the ECMWF ensembles. && .AVIATION...(For the 00Z TAFS through 00Z Saturday evening) Issued at 631 PM EST Fri Jan 8 2021 The latest trend in the low clouds is that they are shifting south of several TAF sites including KGRR...KMKG and KAZO. Based on satellite loops...the lower clouds will soon move south of KLAN and eventually KBTL and 03z. After that it looks like through the remainder of the night the conditions should remain VFR. However...model guidance is trying to reform sub IFR clouds/fog north of KMKG toward daybreak Saturday. If that does is possible for those impactful conditions to track through KMKG and possibly KGRR Saturday morning. Aviators should monitor the latest trends through the period. && .MARINE... Issued at 324 PM EST Fri Jan 8 2021 Winds will be fairly light over the next few days, though by early next week will turn more from the west and increase slightly. This may build waves up to 2-4 feet at times. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. LM...None. && $$ UPDATE...MJS SYNOPSIS...CAS DISCUSSION...CAS AVIATION...MJS MARINE...CAS
National Weather Service Raleigh NC
915 PM EST Fri Jan 8 2021 .SYNOPSIS... An area of low pressure will strengthen and move northeast along the NC coast tonight. Canadian high pressure will return to the region over the weekend. && .NEAR TERM /THROUGH TONIGHT/... As of 900 PM this evening. ...Winter Weather Advisory will be canceled shortly. ...Special Weather Statement will be issued for some isolated or scattered patches of black ice development late tonight in the Piedmont. The latest data analysis and radar trends suggest that the chance of appreciable snowfall for our region is quickly coming to an end. The mid/upper low was elongated and located over the SE Coastal Plain. The most concentrated precipitation area was located just NW-N of the aforementioned mid level circulation currently extending from near Southern Pines to Raleigh to Rocky Mount to Elizabeth City. Even though there has been a change to snow in the spotty higher reflectivity on radar from Moore County NE through Wake and Franklin Counties, the higher reflectivities are drying up from the NW as the mid level low pulls quickly east. The precipitation rates are lightening up from the north with a change back to a light rain/mist as the upper lift/support shifts SE. Therefore, the higher rates will shift into the warmer Coastal Plain very shortly, with rain expected to be mixed with a little sleet and snow as it ends there. The latest RAP indicates that the main precipitation shield will quickly rotate east of the Raleigh and Southern Pines areas before 1100 PM, then exit the Fayetteville, Goldsboro, and Rocky Mount areas by 100 or 200 AM. Since the back-edge of the steady and significant precipitation had already arrived for much of western Piedmont, Triad, Southern Piedmont and portions of the NE Piedmont - there is now a very limited chance (an hour or so) for much more than a brief dusting of wet snow before ending. An isolated slick spot can not be ruled out, but with temperatures expected to remain above 32 and the roads well above freezing, as well - the WSW will be canceled. Some very patchy slick spots (black ice) will be possible later tonight as the skies clear, temps and dew points fall below freezing, and nearly calm conditions will slow the drying process. However, the impact is expected to be limited at the current time - and isolated. Therefore, a Special Weather Statement will follow the WSW instead of another WSW issuance. -Badgett Previous discussion updated at 745 PM. Light snow accumulations may now be confined to brief bursts of heavier snow for the eastern Piedmont and western Sandhills as the upper low passes overhead. Snow already ending in the Triad region as heavier precipitation and upper low shift south and east of Greensboro. The latest radar data suggests that the best chance of light snow accumulations with the ongoing changeover will be within the heavier shower elements noted by reflectivities of 30-35+ dbz. These heavier convective showers will bring brief bursts of snow. These "snow islands" will be found within the larger area of widespread much lighter returns on radar (<25-30 dbz). Note, that the heavier showers or bursts of precipitation are becoming rather limited in coverage as the evening wears on - even with the rain to snow transition that is occurring more rapidly. Given the surface temperatures are likely to remain above 32.0 until after the precipitation ends and that the roads are wet and in the mid 30s to lower 40s - many roads will remain just wet. There may be some black ice potential later tonight, especially where there is a slushy accumulation in the next few hours and where there is lingering water runoff that will potentially freeze - as skies clear and temperatures fall just below 32. -Badgett As of 650 PM this evening. Now snowing along the NC/VA border... and snow continues in the Triad... tapering off in Winston-Salem. We are finally getting a change over to snow from the north into northern Granville, Vance, and Warren counties per Radar. And, the change to snow is occurring in Orange. The main rain/snow lines movement should accelerate in the next few hours with rapid cooling aloft associated with the lift/cold upper low overhead, and onset of nightfall. back edge of the accumulating snow now into Davidson and Forsyth... sadly for snow lovers. -Badgett Previous discussion as of 542 PM Friday... The change-over to snow has occurred in the Triad... rain/snow line extends from High Rock to Asheboro to Burlington to Roxboro... moving slowly southeast. The Correlation Coefficient (CC) off our local radars is now depicting the main/rain snow line... slowly moving SSE through the Piedmont. When used with the radar reflectivity it currently depicts the main rain/snow line extending southwest to northeast... from near High Rock Lake to near Asheboro... to near Burlington... to Roxboro (southern Davidson through central Randolph... southeast Guilford... central Alamance... northern Orange... and central Person. The higher reflectivities are depicting the change-over from rain to sleet or ice pellets. Snow was reported north and west of the line. Reports are coming in of snow beginning to stick in Davidson County (Lexington) and in Person (Roxboro)... and around Greensboro. With temperatures expected to fall to around 32 or 33 with the snowfall (after change-over)... slushy accumulations will begin on elevated surfaces first, then potentially on the bridges/overpasses, followed by the roadways. It continues to appear that there will be a small window of time (~2-3 hours) of high enough snowfall rates in these bands for snowfall to accumulate, before the snow tapers off. Note the downslope flow in Wilkes and Surry Counties (on the back side of the system, now) already reducing the snowfall rates (already ended at Wilkesboro and Mount Airy). This drier air will feed into the Winston-Salem area shortly (already seeing the reflectivity rates with the snow there reducing quickly in NW Forsyth. Since the main rain/snow line depicted by radar is very slow to move... it will still be several hours before any change is likely in the immediate Triangle. Portions of Orange and Durham will see this change-over to snow between 6-8 PM. We will send reports as this transition occurs. -Badgett Previous discussion issued at 415 PM today... The Winter Storm Warning has been replaced by a Winter Weather Advisory. A potent mid-upr shortwave trough over ern GA will pivot newd to near the sern NC coast by 06Z, then offshore overnight. The much-anticipated deformation precipitation band over wrn NC has expanded and strengthened in advance of that trough aloft during the past several hours, indicated by cooling cloud tops in IR satellite imagery and an expansion and increase in radar reflectivity. Hourly liquid equivalent amounts within that expanding precipitation band have likewise increased from a hundredth or two to 0.04"-0.08" in the past couple of hours. Those precipitation rates are expected to continue at times as the deformation band pivots ewd into the wrn Piedmont during the next couple of hours, then ewd across the remainder of cntl NC throughout the evening, with additional liquid equivalent amounts of a couple of tenths likely, locally higher. With only marginally cold boundary layer temperatures likely to limit snow ratios generally to around 8:1, snow accumulation will generally range from 1 to 1.5" over the nw Piedmont, where the Warning was previously in effect, to a coating to locally around an inch throughout the remainder of the Advisory area. While the combination of increasing precipitation rates and loss of insolation after sunset should allow temperatures to continue to cool to between 32-34 degrees beneath the precipitation band and maximum precipitation rates, temperatures may actually rise slightly as the band departs, prior to cooler and drier air now over VA being advected more fully swd overnight - supportive of Sat morning lows in the upr 20s to around freezing. Given those freezing temperatures Saturday morning, patchy black ice will be possible late tonight-early Saturday, particularly on bridges and overpasses. && .SHORT TERM /SATURDAY THROUGH SATURDAY NIGHT/... As of 350 PM Friday... A strongly-sheared shortwave trough in wnw flow aloft over the cntl High Plains this afternoon will dig sewd into the mid-South by 12Z Sat, then off the SC coast by 00-06Z Sun. Associated weak forcing for ascent may result in patches of altocumulus, within an otherwise deeply dry and stable column in the wake of the strong mid level cyclone now crossing the Carolinas. In the low levels, surface high pressure building sewd from the MS Valley will result in nwly flow and weak CAA, with highs mostly in the mid- upr 40s and chilly lows in the mid-upr 20s. && .LONG TERM /SUNDAY THROUGH FRIDAY/... As of 240 PM Friday... Dry and seasonable weather in store for Sunday. Another weather system will move through the Southeast Monday and Tuesday with snow possible once again across the Piedmont... Sunday: Nearly zonal flow aloft over central NC will prevail Sunday and Sunday night as the surface high over the Midwest ridges east into the region. While the primary surface high remains over the Midwest, a smaller area of high pressure is expected to develop east of the Appalachians Sunday night. Expect dry, seasonable weather for the end of the weekend. Highs topping out in the upper 40s to low 50s and lows dropping into the mid to upper 20s. Monday through Tuesday night: The next weather system to impact central NC is moving into the Pacific NW today. A shortwave will break from the parent low and dive southeast through the Rockies and into the southern Plains by Sunday/Sunday night. This wave will continue to track east through the Arklatex on Monday before lifting northeast and east into and through the mid-Atlantic Monday night and Tuesday as the parent trough remains anchored from the Great Lakes to TX. At the surface, high pressure over the area on Monday will be shunted northward as a low develops over the central Gulf Coast in response to the upper wave. As this low develops, a coastal trough will also develop along the Southeast and Carolina coasts on Monday. There are still some model discrepancies with the timing and track of the low as it lifts northeast through the Southeast and along the Carolina coast. The track and how/where the cool air lingers over the NC Piedmont will impact the weather and potential for non-liquid precipitation over the Piedmont Monday night/Tuesday morning. While there is still a chance for some snow, mainly over the Piedmont, confidence is not terribly high at this time. Temperatures will be borderline and will likely require some wet bulbing or heavy rates to get much snow. Will keep snow out of the forecast grids for now, though it cannot be completely ruled out just yet. Wednesday through Friday: This period should once again be predominantly dry and seasonable with surface high pressure ridging into the area in the wake of the low. The upper trough will progress through the eastern US midweek, but with little moisture to work with will keep the forecast dry. && .AVIATION /00Z SATURDAY THROUGH WEDNESDAY/... As of 640 PM Friday... Outside of some brief VFR ceilings at RWI, all other TAF sites to experience IFR conditions to start the TAF period. The mid-level low pressure system has moved further east from its position at 18Z, located over southwest NC. Not much change from the previous forecast, with precipitation tapering off from west to east between 02 and 06Z. Precipitation has changed over to light snow at GSO/INT. However, the back edge of the snow has already started to move near INT. Expecting the light snow over the Triad to taper off at or before 02Z as drier air works in as the low pressure system pushes eastward. VFR conditions will follow shortly thereafter. As for RDU/FAY/RWI, latest model soundings continue to indicate some uncertainty in regards to whether the airmass gets sufficiently below freezing to change precipitation over to snow. Latest radar also suggest a delay in the changeover. Have opted to keep a TEMPO period of a rain/snow mix at RDU/FAY/RWI as a result. VFR conditions will follow between 06 to 08Z. Winds will be light through the period, becoming northwest on Saturday between 6 and 8 knots. Outlook: VFR conditions take over Saturday through the first part of Monday. Another area of low pressure moves into the region Monday night and Tuesday, with the potential for sub-VFR conditions and light rain. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...CBL/MWS NEAR TERM...Badgett/MWS SHORT TERM...MWS LONG TERM...KCP AVIATION...Kren
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