Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/22/16

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
547 PM EST Wed Dec 21 2016 .AVIATION... No aviation issues through the first half of the night, simply a blanket of mid cloud emanating from low pressure tracking through northern Michigan. Low cloud development will require the arrival of a trailing cold frontal passage and subsequent low level saturation expected to commence through the early-mid morning period. Upstream observations across WI/MN suggest a slower arrival time, greater potential for conditions to slip into MVFR now centered 09z-12z. MVFR stratus tied to low level thermal troughing likely persists well into the day Thursday. Modest southerly wind shifts to westerly with the frontal passage. For DTW...entry of a lower stratus now centered 09z-12z. MVFR conditions expected thereafter into Thursday afternoon. //DTW Threshold Probabilities... * Moderate for ceiling falling below 5000 ft Thursday morning. && .PREV DISCUSSION... Issued at 323 PM EST Wed Dec 21 2016 DISCUSSION... Vertically stacked upper wave and surface low pressure over the Upper Midwest still on track to cross Michigan tonight. Weak isentropic ascent so far today has yielded widespread returns on radar but little reported snowfall yet as ascent is still working to overcome dry air observed on 12Z DTX Raob. Isentropic ascent will ramp up very late this afternoon and this evening as the low draws closer and southerly flow increases. This will provide a better chance for light snow to reach the ground, mainly over the Saginaw Valley and Northern Thumb where better forcing and more low-level moisture will reside. Accumulations, if any, will be very light due to fast-moving nature of the system and the dry air preceding it. Would expect to only see a few tenths of an inch of snow at best by midnight. QPF amounts are supported by upstream observations in Wisconsin picking up between a trace and a few hundreths of precip. Locations south of I-69 stand to see only a small chance for a light snow shower or some flurries. Moisture in the dendritic growth zone strips away after midnight behind an occluded frontal boundary. Forecast concern then turns to moisture depth under an inversion, and whether or not we can generate any freezing drizzle. NAM is the most aggressive with low- level moisture, as typical, and will favor the drier RAP and HRRR and leave mention of drizzle out of forecast late tonight through Thursday morning. Clouds and around 10 knots of wind persisting overnight combined with only weak cold air advection should hold temperatures in the mid to upper 20s. Upper ridge centered over the Central CONUS will slide closer to the Great Lakes tomorrow, allowing surface high pressure to begin expanding into the area. This should provide dry weather, although clouds are expected to remain locked under an inversion into the afternoon until some drier air is entrained into the boundary layer. Deeper mixed layer tomorrow will provide slightly warmer temperatures despite some cooling low in the column. Will favor max temps in the mid 30s to near 40. Next potentially impactful item to watch will be a good chance for quick but light snow accumulation Friday night. Energy from the upper low west of Baja California will eject northeast and track across Michigan late Friday into Friday night. Latest model runs are consistent with the system pulling some of the low-level moisture now streaming across Baja into Michigan Friday night as the surface low tracks across Northern Michigan. Track looks far enough north for a rain/snow mix to be possible over the far southeast corner of Michigan as warmer air is drawn into the Southern Great Lakes. Will mention a rain/snow mix south of I-96 for now, with the caveat that some fine-tuning of precip type will be needed as the system draws closer. Precip will occur ahead of a cold front, and event should be a fairly quick one, lasting 6-8 hour at most in any location. Cross- sections from NAM/GFS show a layer from the surface up through 800- 700mb of 3-4 g/kg of specific humidity, even in the coldest air (MBS). These models also suggest a lower snow-ratio event that only generates about an inch of snowfall at best (where precip remains all snow). Given moisture origin and content, cannot discount higher QPF amounts on the Euro/GEM up to 0.25 inches. Snow amounts could need an upward adjustment if higher QPF starts to look more likely, or if thermal profiles trend cooler. Ridging building over the Great Lakes region on Saturday in response to amplifying trough over the Western US will yield milder, drier conditions. Strong low pressure then develops ahead of the trough over the Central Plains on Sunday before moving northeastward over Minnesota Sunday night. While Sunday will start with seasonable temperatures in the 30s, warm air advection will overspread Michigan Sunday night into Monday. As a result, rain/snow mix moving into Michigan on Sunday night will transition to rain until the frontal passage on Monday. As the low moves away from the Great Lakes on Tuesday, high pressure builds in bringing drier but colder conditions with highs returning to the low 30s. MARINE... A weakening low pressure system will track east across Lake Superior tonight, pulling an occluded front through the eastern Great Lakes tonight after midnight. This system will produce some light snow showers in addition to briefly enhanced winds. Looking at the current wind field associated with the low and taking into account the weakening trend, it looks like the models are handling the winds over the lakes pretty well. Wind gusts should peak around 20-25 knots right behind the front with cooler air advecting in upon northwesterly flow on Thursday bringing another wind maximum. This system will lift northeast as strong high pressure system slides across our south toward the mid Atlantic states by Friday. The next system will lift through the western Great Lakes on Friday night and Saturday putting our area in the tighter gradient in between the two systems. Increasing stability should keep the potential wind gusts tempered below 30 knots. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...NONE. Lake Huron...NONE. Lake St Clair...NONE. Michigan waters of Lake Erie...NONE. && $$ AVIATION.....MR DISCUSSION...HLO/JD MARINE.......DRK You can obtain your latest National Weather Service forecasts online at
Area Forecast Discussion...UPDATED
National Weather Service Gray ME
1054 PM EST Wed Dec 21 2016 .SYNOPSIS... An Alberta Clipper will swing through the region on Thursday bringing light snow accumulations throughout the region. Behind this system...high pressure will bring dry and seasonable conditions to end the week. Another fast moving weather system will bring a potential round of snow or mixed precipitation on Saturday with seasonably mild temperatures and dry weather expected for Christmas and into Monday of next week. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/... Update...Again no major changes to the current forecast. Have tweaked temps up some in the near high clouds invading from the W are limiting cooling at the moment. Low temps should eventually come as a result of evaporational cooling as precip tries to break out near sunrise. Taking a peek at upstream obs...snowfall seems on pace with the latest HRRR forecasts. These get snow into Wrn zones by 10 or 11z. This matches likely PoP in our forecast I see no need to make any major adjustments there. Snowfall amounts are also in line with the higher end of modeled QPF. I could see a slight increase in QPF across the forecast area to around 0.15 to 0.20 inches. Overall though this is not a significant increase in snowfall amounts forecast for the area. There are some mixed signals from mesoscale model guidance this afternoon. The highest resolution sources favor the largest accumulations across central NH and the White Mtns. The lower resolution versions tend to place that snowfall across Srn NH. There is good agreement of QPF however...with around a quarter inch looking like the maximum output for this fast moving wave. That leaves the forecast in good shape with 1 to 2 inches and an isolated higher total in the mtns. Previous discussion...High Impact Weather Potential: Light snow develops towards daybreak. Current Pattern: Early afternoon water vapor imagery shows broad troughing over the eastern half of NOAM....with one very moisture starved shortwave over New England as of this writing...with a more impressive...yet still moisture-starved shortwave upstream moving into the Great Lakes region. Between these features is a region of shortwave ridging...with an attended high pressure ridge axis at the surface. This feature will control our weather through much of the overnight before the flow backs ahead of the upstream shortwave and top-down saturation commences...with some snow likely to develop over western locations by the very end of the near term forecast period. Through this evening: Initial shortwave is now passing east of our longitude...and had been responsible for a build up of clouds upstream of the mountains of New Hampshire and western Maine...with a few snow showers...but little else. I don`t expect much in the way of changes through this evening...with clear skies south and east of the mountains allowing temperatures to start dropping rapidly from their mild afternoon highs in the 30s to around 40 back into the 20s to around 30 by 7pm. Afternoon westerly winds will diminish markedly by sunset. Tonight: Height rise center associated with shortwave ridge axis moves though the region for the first half of the night before warm advection and associated top-down saturation develops. Thus...expect temperatures to drop quickly in the evening /with some bust potential on just how low they go...but some teens possible/ before leveling off and likely rising towards daybreak. Antecedent airmass is dry...but not terribly have no reason to stray much from model consensus arrival time of precipitation of 4-6am over NH...moving after the daybreak for all but extreme western Maine. Temps certainly cold enough for snow all locations through daybreak. Less than one inch of snow by daybreak over NH is expected. && .SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/... High Impact Weather Potential: Period of light snow Thursday. Pattern: Great lakes shortwave sharpens somewhat as it moves overhead during the day Thursday...with a very weak surface reflection deepening once QG forcing for ascent reaches the waters of the Gulf of Maine. While this coastal low will strengthen will be too little too late for much of a significant impact over our forecast area. However...a period of warm advection Thursday morning in the presence of -DIVQ will yield a period of light precipitation for much of the day. Shortwave ridging and associated surface high builds in Thursday night...with quiet weather to end the short term forecast period. Thursday: Upstream clipper will be located near Georgian bay Thursday morning before moving into northern New England by afternoon with a new low getting it/s act together towards evening in the Gulf of Maine. Upper forcing for ascent is modest...with -DPVA/height falls associated with positively tilted shortwave...but poorly placed jet and limited moisture paints a picture of generally light precipitation due primarily to FGEN/isentropic upglide. QPF/Snow: Given very meager PWATs to work with /generally less than one third of an inch/...and fast moving nature of clipper...this will not be a prolific precipitation producer. Model consensus favors about 0.10-0.15" liquid...which seems very reasonable...with about 6 hours of precipitation expected for any location. Vertical profiles do suggest decent snow:liquid ratio potential... with vertical motion centered within and just above the dendritic growth zone. Cobb algorithm suggests ratios near 14-15:1 away from the cost. Ptype: As indicated by previous shift...likely that nearly all precipitation that falls will be snow. Wet bulbs near 34-35F along the coast by late morning suggest that some rain may mix precipitation comes to an end...limiting coastal accums a tad. A look at SREF and NCAR ensemble plumes yields a few members up to 3" over inland areas and see this as the upper limit for snow. Timing will be problematic for the commute...with all of NH and some of western Maine likely seeing snow begin by 7am. Will continue mention in the Hazardous Weather Outlook and could foresee a SPS down the road...but no headlines warranted given these amounts. Thursday Night: High pressure builds into the region with building heights aloft arriving after midnight. Cold advection behind Thursday/s low will be rather meager...with a seasonably mild overnight expected. Good gradient through much if not all of the night with 1000 mb geostrophic winds remaining 15-25kts...which should keep all but the more sheltered valleys coupled. Thus...expect a few spots to drop into the upper teens...with 20s for most locations. If the wind dies off a bit sooner than expected...more widespread teens are likely. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... Models are in decent agreement on the longwave pattern through the end of the calendar year. We begin the period with a fast low amplitude flow. However...digging shortwave energy entering the pacific northwest will quickly carve out a deep trough over the western third of the CONUS for the start of the upcoming weekend. Downstream we`ll initially see rising heights and a warming trend and rather quiet weather for the holiday weekend. By early next week...we`ve transitioned to a high amplitude progressive pattern that portends a stormy end to 2016. In the dailies...high pressure builds by to our south Friday and Friday night with quiet weather and seasonable temperatures. On Saturday...a passing shortwave will drive an associated cold front across the area with a few snow and rain showers with p-type driven by boundary layer temperatures. Rising heights take over with a ridge of high pressure traversing the area for Sunday into early Monday. A potent shortwave and associated surface low will track from the northern plains and western Great Lakes on Monday into eastern Canada Tuesday. The warm front from this system will bring some light overrunning precipitation to the area late Monday and Monday night followed by a cold front early Tuesday. In the wake of this system...gusty winds along with some upslope snow showers across the higher terrain for Tuesday and Tuesday night. Rising heights and a ridge of high pressure arrive by midweek. A deep trough and associated storm system arrive for the tail end of the work week with a mixed precipitation event for the region followed by sharply colder temperatures and a few mountain snow showers to ring in the new year. && .AVIATION /04Z THURSDAY THROUGH MONDAY/... Short Term... Summary: A fast moving area of low pressure will bring deteriorating flying conditions for the day Thursday before high pressure moves back into the region Thursday night. Restrictions: VFR through the first half of tonight. Snow arrives over NH terminals by daybreak Thursday with a roughly 6 hour period of LIFR/IFR vsbys that moves east with time. VFR conditions return Thursday afternoon/evening and continue through Thursday night. Winds: Westerly winds around 10kts this afternoon will go light/variable overnight and remain less than 10kts through the day Thursday from the southwest. Winds shift northwesterly Thursday night 5-10kts. LLWS: Not expected through Thursday Night. Long Term... Sat...Areas of MVFR in -shsn/-shra. Mon PM - Tue AM...MVFR with areas of IFR -ra/-pl/-sn. && .MARINE... Short Term... Winds/waves will continue to subside through this evening...then all is quiet through Thursday as a clipper system moves over the region. This system will spawn a stronger low over the Gulf of Maine that will strengthen as it departs the region Thursday night. This will bring renewed SCA conditions over the outer waters due to northwesterly winds. Long Term... Fri...Small Craft conditions possible outside the bays. Sat...Gale force winds are possible. Sun...Small Craft conditions possible. Mon PM - Tue...Gales force winds are possible. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...None. && $$ NEAR TERM...Legro