Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/10/20

Area Forecast Discussion
National Weather Service Burlington VT
951 PM EST Wed Dec 9 2020 .SYNOPSIS... Snow is expected to continue this evening, and become confined to the higher terrain on late tonight into tomorrow. Dry weather returns on Friday but precipitation chances will be increasing during the latter part of the weekend. The leading edge of precipitation could produce a brief wintry mix late Saturday evening, which will transition to all rain heading into Sunday. The weather system on Monday with lingering, terrain driven shower activity becoming snow. Then a brief dry period is expected Tuesday into much of next Wednesday. && .NEAR TERM /THROUGH THURSDAY NIGHT/... As of 948 PM EST Wednesday...Forecast continues to remain in good shape. Area webcams and radar show scattered light snow showers across the area, mainly confined to the western slopes and higher terrain, northeastern Vermont and the northern Champlain Valley. Things should continue to taper off over the next several hours with between a dusting and half inch expected by sunrise. No real changes to the forecast were needed. Previous Discussion...Not much has changed as light snow composed of fine crystals continues to fall. The forecast remains generally on track, though snow has continued to struggle to make its way into eastern Vermont. We should see increasing lift as a result of cyclonic vorticity advection over the next few hours, and forecast soundings suggest we become supersaturated with respect to ice with deepening snow growth zones. This should result in some better dendrites. However, surface temperatures have warmed to right around freezing, which could make accumulating a bit more challenging. Driving is likely a bit slick where roads are untreated with pavement temperatures right around 30 F over Vermont. RAP mesoanalysis depicts a relatively thin axis of better moisture in the DGZ and there`s not much in the way of forcing for ascent, which is supportive of continued light snow. Pocket of 700mb moisture begins to thin, tonight. Snow showers becoming lighter and confined to the high terrain. Temperatures are not likely to fall much this evening with no real change in airmass and abundant clouds. Thus, lows around 30 are expected. Any lingering snow showers in the valleys should end early Thursday morning, and then we should see snow finally exit the mountains by noon, with the last vestiges in the Northeast Kingdom thinning near 3 PM. Surface high pressure will sit to our south, but it has a ridge axis that extends northwards to our west that will keep our winds out of the northwest most of the day. This should keep temperatures in the 30s. Pockets of high clouds will skirt the region, and winds should gradually turn out of the south overnight on Thursday. This will keep lows from falling too far. Expect mid 20s in the valleys, and upper teens to around 20 across cold hollows. && .SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/... As of 317 PM EST Wednesday...Forecast will trend warmer for Friday as ridging off the Mid-Atlantic Coast shifts eastward and return southwesterly flow develops over the North Country. Highs will be in the upper 30s to mid 40s throughout the area. The day will start off with a few breaks in the low clouds and some peaks of sun, but by the afternoon hours will see more low clouds work into the area as several weak frontal boundaries move through. May see a few light rain/snow showers during the afternoon and evening hours Friday, but the majority of the period will be dry. Low clouds with the potential for a scattered light shower or two will persist into the overnight hours. Lows will be in the upper 20s to low 30s. && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... As of 317 PM EST Wednesday...Continuing to watch a low pressure system in the long term forecast that will impact the forecast area this weekend. The low will initially form over the southern Plains Friday, lifting northeastward through the MidWest and then weakening as it travels into Ontario/Quebec by Saturday into Sunday. This track would keep our forecast area mainly in the warm sector of the cyclone. Initial warm front will push through Saturday afternoon into Saturday evening, with some potential for a quick shot of some messy mixed precipitation. Still a little early to get a proper handle on surface temperatures and the evolution of the warm nose associated with the system, which will directly impact icing potential. However, can`t rule out a favorable thermal profile for some freezing rain, especially Saturday evening. Have kept mention of any freezing rain out of the forecast at this point with too much uncertainty around temperatures in the lower-levels, but will continue to watch trends and may need to add it in in subsequent forecast packages. Temperatures will warm through Saturday night to near to above freezing throughout the forecast area, so will see a period of rain for the bulk of the event Saturday night through Sunday as we are solidly in the warm sector of the cyclone. The system`s cold front will move through late Sunday/early Monday night, allowing for a transition to some waning snow showers on the back edge of the system. Overall, main threat of the system that we will continue to watch will be the icing potential for Saturday evening. No hydro concerns at this point and, given the weakening nature of the system as it tracks into Canada, not seeing much of a wind threat either. The weather will turn drier as we head into next work week with a cooling trend going into midweek. && .AVIATION /03Z THURSDAY THROUGH MONDAY/... Through 00Z Friday...Light snow continues in the Champlain valley, and is slowly coming to an end across the rest of our area. Most locations still have MVFR ceilings, despite snow showers coming to an end. Exceptions are SLK which is IFR and PBG which is VFR. Will take awhile for ceilings to improve, likely staying MVFR through the overnight. Snow showers will linger the longest at BTV and SLK. Winds are currently southerly and will be veering around to westerly overnight. Remaining snow showers should dissipate around 12-15Z, and we will see ceilings begin to improve as well towards 2500-5000ft agl. Outlook... Thursday Night: VFR. NO SIG WX. Friday: Mainly VFR, with local MVFR possible. NO SIG WX. Friday Night: Mainly MVFR, with local IFR possible. NO SIG WX. Saturday: Mainly VFR, with local IFR possible. Chance RA, Slight chance SN. Saturday Night: Mainly MVFR and IFR, with areas VFR possible. Likely RA, Likely SN. Sunday: Mainly MVFR, with areas IFR possible. Likely SHRA. Sunday Night: Mainly MVFR, with local VFR possible. Chance SHRA, Chance SHSN. Monday: Mainly MVFR, with local VFR possible. Chance SHSN, Slight chance SHRA. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...Haynes NEAR TERM...Haynes/LaRocca SHORT TERM...Duell LONG TERM...Duell AVIATION...Haynes/Neiles
Area Forecast Discussion
National Weather Service Louisville KY
907 PM EST Wed Dec 9 2020 .Forecast Update... Issued at 905 PM EST Wed Dec 9 2020 Model time-height sections from the GFS and to a lesser extent the RAP show a deck of mid to high-level clouds coming into the region late tonight. Looking at upstream satellite imagery, starting to see some formation over Missouri and Arkansas. As the night goes on, model RH fields show increasing saturation in the 200-400 mb layer, particularly the GFS1hr. CMCreg/NAM/RAP are not as wet, so will just go with a scattered high deck for now. The other concern to watch for is fog formation. Statistical guidance is not too gung ho on the potential, but they do show some conditional category 1`s for ceilings, indicative of a very low cloud layer that sometimes can be fog. Will focus on areas west of I-65 for the next couple of hours for patchy fog potential, but then as some high clouds build in, think it will shift to patches more east of I-65. && .Short Term...(This evening through Thursday) Issued at 251 PM EST Wed Dec 9 2020 Things remain quiet in the short term with dry and notably mild conditions continuing. Current NW flow aloft will transition to a brief zonal flow tomorrow, with only some upper clouds around at times. Skies should be mostly clear overnight, and with light and variable winds the good radiational cooling could allow for some patchy fog development. Have included this fog mention mainly east of I-65. Otherwise, expect lows in the low to mid 30s in most spots. Highs on Thursday are expected to be even milder than today, with the mercury topping out in the 60 to 65 degree range in most spots. Our NE CWA could hang onto the upper 50s, but still a couple degrees milder than we are seeing today. .Long Term...(Thursday night through Wednesday) Issued at 235 PM EST Wed Dec 9 2020 Friday continues to look like the warmest day of the 7-day forecast period as the region sits well within the warm sector of a warm front that will be near the Great Lakes region. While clouds will gradually increase through the day Friday, modest southwesterly flow should result in high temperatures climbing into the low and mid 60s. Showers and even a few rumbles of thunder will move in for Saturday and persist for a good portion of the day. Despite the widespread rain showers and clouds, temperatures will remain fairly mild until the front passes through, which may not occur until closer to Saturday evening. Long range guidance has started to come into better agreement for the Sunday through early next week timeframe. Appears now that any systems that develop in the Gulf will be suppressed far enough south to limit any meaningful precipitation chances and accumulations in central Kentucky. Will still hold on to some low-end PoP chances for portions of central Kentucky during this time since guidance could shift things again in the near future, but current trends suggest drier/cooler weather to prevail after Saturday`s fropa. && .Aviation...(00Z TAF Issuance) Issued at 630 PM EST Wed Dec 9 2020 Nice night across the region with winds starting to become more light and variable. They should become southeasterly later tonight and then southerly during the day Thursday. We`ll see a deck of higher clouds move into the region overnight. Even with that deck there still are some question marks with regard to fog potential early Thursday. Have gone ahead with HNB/LEX tempo groups for MVFR visibilities, given a weak signal in LAMP probability guidance and forecast low temperatures a little cooler than this afternoon`s minimum dewpoints. && .LMK WATCHES/WARNINGS/ADVISORIES... IN...None. KY...None. && $$ Update...RJS Short Term...BJS Long Term...DM Aviation...RJS
Area Forecast Discussion...UPDATED
National Weather Service Chicago/Romeoville, IL
827 PM CST Wed Dec 9 2020 .UPDATE... 827 PM CST The forecast updates for this evening have only been a nudging down of the low temperatures in some spots and tweaks to sky cover, the latter of which has a touch more emphasis than usual with a chance for seeing the aurora borealis (Northern Lights). The inclusion of patchy fog into the forecast remains warranted too, so no changes there. A clear early evening with surface high pressure sprawling in provided rapid decoupling. Both Aurora and Rochelle airports already dropped to 30 degrees as of 3 p.m., quite a fall from 3 p.m. readings in the lower 50s. A patch of some translucent to somewhat opaque cirrus near 20,000 ft is over the northeastern quarter of Iowa and drifting toward the area, but satellite imagery has indicated a gradually thinning trend. Some cirrus behind this toward Minneapolis was sampled well by the MPX 00Z sounding and indicated the moist layer being quite thin. So while some cirrus is likely to drift over the area along/north of I-80 between 10 p.m.-3 a.m. and possibly temporarily obscure a sky view, it looks like the cirrus may be often somewhat thin and not to persist that entire time over any one place. Temperatures may wobble some under those clouds, but did lower lows a bit given trends, and expect there to be several outlying sites to reach the mid 20s. VWP data indicates in the past couple hours the winds having really fell off above the inversion, and the RAP forecast hydrolapse indicates a favorable profile for shallow fog. Despite the sharp temperature fall, dew points have generally been falling too though. With the cirrus drifting overhead for part of the area, that looks to probably limit any widespread fog threat, at least that to majorly public-impacting. Some patches of fog to dense level are certainly possible in this regime, especially if the cirrus presently over southern Minnesota does not make it here intact thus yielding more clearing in that 2-6 a.m. time. MTF && .SHORT TERM... 340 PM CST Through Thursday night... Quiet weather will prevail through Thursday as upper ridging builds overhead. The main concern in the short term is the potential for shallow ground fog tonight, especially outside of the metro. Clear skies have allowed temperatures to warm steadily into the low to mid 50s across the area today. Have nudged up overnight low temperatures accordingly. There still remains a fairly decent signal, especially in the hi-res guidance for shallow ground fog development overnight into tomorrow morning. Surface high pressure will be centered over the area with light winds and clear skies. Have introduced a patchy fog mention with this forecast package, although this could be a bit conservative. Will continue to monitor the potential for greater coverage. Given the warmth from today, expect another warm day on Thursday with high temperatures in the low to possibly mid 50s. The upper ridge begins to shift to the east Thursday night with a dry cold front also moving through the area. Expect clouds to increase behind the front as our next system approaches from the southwest. Petr && .LONG TERM... 313 PM CST Friday through Wednesday... The primary forecast challenges in the extended period continue to focus on the evolution of a storm system that is likely to impact the area late Friday through Saturday night. This storm system promises to bring a significant amount of precipitation to the area, but mainly with most of it falling as rain over central and eastern IL into northwestern IN. However, the potential exists for significant snow accumulations for at least parts of far northwestern into far north central IL and points northward into WI. Therefore, we could see a very sharp gradient between significant snow, and little to no snow somewhere right across northern IL, possible even nearing parts of the western/ northwestern suburbs of Chicago. Model and ensemble guidance is in decent agreement with surface low pressure taking shape over the southern Plains on Friday in response to the approach of the upper level low currently off the Baja of California coast. The exact track of the surface low is always key to determine where the accumulating snow will fall. Current indications continue to support a northeast track of the low from near STL early Saturday morning, to northwestern IN early Saturday afternoon. This track, would favor the main area of accumulating snowfall to be roughly across my northwestern areas, namely the Rockford metro area and possibly as far southeast as parts of the far northwestern Chicago suburbs. Mainly a rain event looks to be in store for much of the rest of the region. We will have to continue to watch this closely as even a minor shift in the expected track could change this scenario, so stay tuned! While the placement of heaviest snow accumulations continues to be unclear, there is high confidence in a good amount a precipitation over the area late Friday through Saturday evening. As noted in previous discussions, an impressive northward surge of Gulf Moisture is expected with the approach of the area of low pressure. This is noted by precipitable water values progged to climb to near 1" over southern sections of the area, which is above the 90 percentile for this time of year. This in combination with what looks to be good upper level jet support, with the possibility for upper level jet coupling all point towards an impressive precipitation event for the area. For these reasons, widespread amounts of 1 to perhaps close to 2 inches of liquid equivalence is probable across the area through Saturday night. The precipitation looks to onset across the area Friday late morning and into the afternoon following a surface cold frontal passage. A lower level baroclinic zone will then sag over the area setting the stage for rain to develop during the day. The rain then looks to mix with and change to snow by early Friday evening somewhere over far northern IL and then continue at times through Saturday as the column cools. The period of heaviest precipitation looks to be from late Friday night through the mid afternoon hours on Saturday as the best dynamics line up overhead. The precipitation then looks to gradually come to an end from west to east Saturday night into early Sunday morning, likely ending as a little snow for most areas, though with little accumulation. Some potential will exist for some weak lake effect into parts of northwest IN through midday Sunday, though forecast soundings indicate rather unimpressive parameters with no real arctic air intrusion and it currently looks as if winds should turn northwesterly enough by afternoon behind the departing system to shift any threat east of our forecast area. Though models continue to show some significant details with the pattern early next week, a couple days of seasonably colder weather appear in store for the region Monday and Tuesday as weak surface high pressure spreads into the area. One other note with the weekend storm, is that as winds turn northerly and increase late Friday night through Saturday, there may be a period of lakeshore flooding potential along the IL and IN shores of Lake Michigan. The greatest threat, with waves 8+ feet, would likely be Saturday afternoon and evening. KJB/Ratzer && .AVIATION... For the 00Z TAFs... 514 PM CST * Only item of note is possible MVFR BR at outlying terminals Mainly quiet aviation conditions are in store for the next 24-30 hours. Patchy FG/BR appears probable south and west of the terminals late tonight into Thursday morning. Best chance for IFR VSBY is south of the outlying TAF sites. Maintained TEMPO MVFR VSY at DPA, RFD, and GYY. Chicago sites should stay VFR. Light/VRB winds will become south and pick up some mid-late Thursday morning. Some mid to high teens kt gusts are possible in early to mid afternoon. Castro && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...None. && $$ Visit us at Follow us on Facebook, Twitter, and YouTube at:
Area Forecast Discussion
National Weather Service Marquette MI
645 PM EST Wed Dec 9 2020 .SHORT TERM...(This evening through Thursday) Issued at 403 PM EST WED DEC 9 2020 WV imagery and RAP analysis indicated a split flow pattern with mid/upper level ridging through the Plains and wnw flow prevailing through the northern Great Lakes. Upstream shortwave troughs were moving through southern Saskatchewan and into northwest Montana. At the surface, northwest winds persisted between a trough over Quebec and high pressure building eastward from the Plains. Vis loop showed clear skies over most of Upper Michigan with clouds slowly receding over the east. Additional mid/high clouds supported by the developing WAA pattern were quickly spreading ese through northern MN. Tonight, with the ridge building into the area and a period of clear to partly cloudy skies, temps should drop off into the low to mid 20s inland with readings closer to 30 near the Great Lakes. If the mid clouds thicken more quickly overnight, temps may slowly rise late. Potential northern lights viewing may also be complicated by the clouds moving in near or after midnight. Thursday, as the northern stream shrtwvs and western Dakotas sfc trough approach with moderate to strong 290k-300k isentropic ascent, pcpn should also expand from far ne MN into northern Lake Superior. However, expect the pcpn to remain north of the the all but the tip of the Keweenaw where slightly chance POPs for rain/snow was mentioned. Winds veering to the northwest late in the day as the trough moves in could also bring some light lake enhanced pcpn to the Keweenaw. Otherwise, expect continued mild conditions with mild southerly flow ahead of the trough with highs in the low 40s. .LONG TERM...(Thursday night through Wednesday) Issued at 343 PM EST WED DEC 9 2020 The medium to extended forecast period will usher in a split flow regime where the polar jet assists with surface low pressure development north of the area, and the subtropical jet will assist with mid-latitude surface low pressure development to the south of the area through the weekend. This isn`t to say we will have no weather over the area at all, but a phased signal would need to be achieved with deep troughing over the central and northern CONUS for impactful weather to occur in our CWA. Ensembles from the GEFS and GEPS do begin to signal more troughing over the CONUS from this weekend through portion of next week, but is not expected to assist with cyclogenesis directly over the CWA during this period. Looking more in depth for the forecast brings to light a few details to note. A shortwave trough Thursday night through Friday morning will bring in colder surface temps behind a cold front. Model soundings show low level saturation through approximately 3-5kft before the inversion takes hold and dry air infiltrates the area. Precipitation chances look low at this time to include in the local forecast. The cold front will be on the order of approximately 7-10 degrees colder for Friday afternoon highs compared to the previous day. The next weather disturbance of note to mention will be the evolution of the surface low as lee-side cyclogenesis begins to occur over the rolling plains of TX/OK Friday. This surface low is expected to deepen by approximately 10mb over the course of Friday morning through Saturday afternoon as it treks to the northeast over the Great Lakes region. Model consistency has been congealing into a better signal the last 24-36 hours, but the latest iteration of the 12Z NAM has introduced an interesting possibility albeit as the outlier to other guidance. The 12Z NAM has the surface low center just east of Cedar Rapids, IA instead of the southern tier of Lake Michigan by 0Z Sunday. This is about 200 miles further to the west of the other guidance solutions for a surface low center, and could present the opportunity for more accumulating snowfall on our southern portions of the CWA if the surface low continued to propagate northeast from there. However, did not change forecast evolution with regard to snowfall chances yet due to it not lining up with other guidance, in addition to the 84 hour limit for the NAM. Wrap around winds will likely create some lake effect snow showers for the CWA, but snowfall totals will be limited based off the present guidance available. For Monday through the middle portion of next week, an additional shortwave disturbance is anticipated to move over the Great Lakes area. 850mb temps looks cold enough to support an all snow event for the lake effect snowbelts, but will be conservative on the forecast as this is 120+ hours out as of this forecast package issuance. && .AVIATION...(For the 00Z TAFS through 00Z Thursday evening) Issued at 644 PM EST WED DEC 9 2020 VFR conditions are present at all terminals, but mid level clouds are moving into the area and should fill in overnight. The feature of note during this TAF period is a cold front expected to move across the area late Thursday afternoon and into Thursday evening. The cold front should abruptly end the prolonged period of VFR cigs. && .MARINE...(For the 4 PM Lake Superior forecast issuance) Issued at 403 PM EST WED DEC 9 2020 NW winds will subside below 20 kts this evening as a high pressure ridge passes by to the south. Thursday night a cold front will sweep across the lake bringing more 20-30 kt NNW winds into Friday morning. After that, Saturday remains the next period to watch. Models seem to have settled on a farther south track with the low pressure system that will be moving through the Great Lakes, which means NE winds Saturday and Saturday night should remain in the 20- 30 kt range with gales looking unlikely. Winds are expected to back around to NW and relax below 20 kts for Sunday. && .MQT WATCHES/WARNINGS/ADVISORIES... Upper Michigan... None. Lake Superior... None. Lake Michigan... None. && $$ SHORT TERM...JLB LONG TERM...BW AVIATION...EK MARINE...JLB