Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 04/05/18


Area Forecast Discussion
National Weather Service La Crosse WI
607 PM CDT Wed Apr 4 2018 .SHORT TERM...(Tonight and Thursday) Issued at 240 PM CDT Wed Apr 4 2018 Skies were clear this afternoon as a surface ridge axis was moving east toward the Upper Mississippi River Valley. As the high continues to slide off to the east this evening, expect a couple disturbances to bring small rain/snow chances to the area tonight into Thursday. First, a mid-level wave is forecast to move across northern Iowa later tonight. There may be enough warm-air advection/isentropic lift to produce some flurries or light snow, but saturating the column will be challenging given the very dry low-level air. Low chances for precipitation will continue with the mid-level wave as it moves into southern Wisconsin on Thursday. Meanwhile, a stronger shortwave currently over southwest Saskatchewan will approach northern and central Wisconsin by Thursday evening. Precipitation looks a little more likely with this system. The timing of this wave in the 04.12Z Extended HRRR is much quicker, but that solution is currently an outlier. Temperatures will remain well below normal as the northwest flow pattern continues. Some locations in central Wisconsin could see lows tonight approach zero degrees Fahrenheit. .LONG TERM...(Thursday Night through Wednesday) Issued at 240 PM CDT Wed Apr 4 2018 Exiting short wave could still be producing a brief period of light precipitation Thursday evening, but exiting is the key word as even colder air advects in. Large area of high pressure /ridge/ builds in for first part of the weekend so lowered minimum temperatures in favored cold spots where winds could decouple and snow pack will allow big drops. Of far more importance is what could be very busy week ahead according to medium range guidance. Possibility of 3 weather events to impact region so will have to take them one at a time. Event 1 comes in Sunday afternoon as mid level wave transverses region. Favorable lift region ahead of this system should make for widespread precipitation that shifts through overnight. A bit far out for details, but thinking guidance might be too warm which would account for more snow than rain/snow mix. Either way could see more snow accumulations and perhaps into advisory criteria? Again, details will need to be worked out as event approaches. After quick revive Monday night and Tuesday, an even stronger short wave moves through increasingly more active flow for midweek. With warming temperatures, could see more of a precipitation mixture than weekend event, but too far out for specifics. With snow pack and pattern becoming more active /and warmer/ will need to keep an eye out for flooding concerns or impacts. && .AVIATION...(For the 00Z TAFS through 00Z Thursday evening) Issued at 607 PM CDT Wed Apr 4 2018 Generally expecting VFR conditions through Thursday. A short wave trough currently over the western Dakotas will slide southeast and slip just south of both airports Thursday afternoon. Some light precipitation should develop with this wave, but it too should stay to the south of both airports. Another short wave trough, currently over southern Alberta, will also slide southeast and should be moving across central Minnesota by late Thursday afternoon. The light precipitation associated with this wave should still be to the northwest of the area. However, there will be enough of an increase in moisture from these waves to bring in a VFR ceiling for Thursday afternoon to both sites. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...None. MN...None. IA...None. && $$ SHORT TERM...Hollan LONG TERM...Shea AVIATION...04
Area Forecast Discussion
National Weather Service Green Bay WI
1012 PM CDT Wed Apr 4 2018 Updated aviation portion for 06Z TAF issuance .SHORT TERM...Tonight and Thursday Issued at 304 PM CDT Wed Apr 4 2018 The latest RAP analysis and satellite/radar imagery show an area of strong low pressure moving across northeast Ontario while a relatively weak surface ridge axis extends north over the northern Mississippi Valley. Skies are mostly clear except for the northern Door Peninsula where the back edge of the cyclone`s cloud shield is in the process of exiting. Looking upstream, a weak, channeled shortwave is moving into the boundary waters of Minnesota early this afternoon. Cloud bases remain relatively high with this system, and have only seen isolated reports of flurries. As this system moves across the northern Great Lakes tonight, and another system approaches the region tomorrow afternoon, cloud trends and small precip chances are the main forecast concerns. Tonight...The surface ridge axis will shift southeast across the state at the same time as channeled vort energy slides across far northern WI and the Upper Peninsula. Some clouds will likely move into northern WI during the evening, but though deep moisture is generally lacking, models show that precip chances will remain north of the U.P. border. This makes sense given the very low dewpoints that moved into northern WI by early this afternoon. Despite the ridge axis arriving, winds may struggle to decouple in spots. Combined with some clouds, low temp forecast is tricky. Did edge temps a degree or two lower though, mostly due to the fall of dewpoints so far today, and believe there could be enough clearing for temps to tank in the cold spots. Lows ranging from around 5 above at Tomahawk to the mid teens near Lake Michigan. Thursday...Once clouds depart far northeast WI early, should see some sunshine for the rest of the morning. Then clouds are expected to increase again from west to east as a slightly more potent shortwave moves into the state during the afternoon. Moisture will remain limited, but precip chances look to return to central and north-central WI by late in the afternoon, which may be slightly slower than the previous forecast. Temps will be cold enough for mainly snow over the northwoods, and a rain/snow mix over central WI. Winds will shift to the southwest, which should result in warmer temps. Highs returning to the middle 30s. .LONG TERM...Thursday Night Through Wednesday Issued at 304 PM CDT Wed Apr 4 2018 The main concern for this period will be the well below normal temperatures through the weekend. The system pushing through the area beginning on Thursday will also continue into early Friday morning with chances for snow. Another system will cross the area Sunday night into Monday. Guidance is in agreement for timing and p-type for the system on Thursday continuing into Friday morning. Minor snow accumulations are possible. Some areas in north-central and central Wisconsin may see higher amounts of 1 to 3 inches of snow. Cold air will drive into the area behind this system allowing temperatures on Friday to fall well below normal. Temperatures will remain 10 to 20 degrees below normal into early next week as well. It is also possible, if conditions become clear and calm, temperatures can drop very quickly to the single digits below zero. The system for Sunday night into Monday shows some uncertainty between models for the timing of the precipitation and the axis of the low pressure system track. This results in uncertainty in p-type and accumulations across the area. Therefore, a standard blend of model guidance was favored for the forecast. && .AVIATION...for 06Z TAF Issuance Issued at 1011 PM CDT Wed Apr 4 2018 VFR sct-bkn clouds will drift over northern Wisconsin overnight, otherwise VFR conditions expected overnight into Thursday. Mid level clouds will be on the increase Wednesday afternoon and early evening as a short wave approaches the area from the northwest. Scattered MVFR clouds and vsbys due to snow may spread over the area later Thursday evening. && .GRB WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM.....MPC LONG TERM......Hykin AVIATION.......TDH
Area Forecast Discussion
National Weather Service Grand Rapids MI
937 PM EDT Wed Apr 4 2018 LATEST UPDATE... Update .SYNOPSIS... Issued at 310 PM EDT Wed Apr 4 2018 One area of low pressure will track away from the region tonight taking the snow showers and wind with it. A weak area of high pressure will track through on Thursday resulting in mainly a dry and less windy day. Yet another storm system quickly tracks through Thursday night resulting in another round of snow. A cold airmass then spreads in for the weekend. && .UPDATE... Issued at 937 PM EDT Wed Apr 4 2018 Clouds and flurries were still hanging on this evening although much of northern and central Lwr MI has cleared out. With sfc ridging moving in would expect to see winds diminishing and the clearing becoming more widespread, especially inland. The latest RAP RH guidance supports this notion. It may be tough to lose the clouds completely however as the cold h8 temps around -13C should continue to generate some lake effect clouds. Will lower min temps up north where it`s already cleared out and a decent snow pack exists. Lows around Leota could end up being in the single digits. && .SHORT TERM...(This evening through Friday night) Issued at 310 PM EDT Wed Apr 4 2018 The snow showers will continue to diminish this evening as the storm system pulls away and the low level convergence weakens. Will hold onto a low risk for snow showers. Well below normal temperatures are expected with values in the upper teens to low 20s for most places. These values are over 10 degrees below normal. With fresh snow on the ground...even colder values are possible...especially for the northern zones. Above freezing highs are forecasted on Thursday as the next storm nears from the west northwest. As the shield of precipitation starts to move in late in the day...there could be a r/s mix at the onset...but that should not last long. Wet bulbing should support a mainly snow event for the region Thursday night. This could change if the storm tracks further north than currently forecasted. There is a convective look to some of the models with this event...which does raise some concern as far as amounts go. Right most of the guidance suggests a 1 to 3 inch snowfall. There are some solutions that give the region almost no snow. The precipitation will not last long as this storm will be moving rather quickly. By daybreak Friday the steady area of snow should be off to the east. Good mixing should support windy conditions on Friday. The dgz moistens back up in the cold airmass later in the day with the winds veering with time. The airmass will be cold enough for lake effect going into Friday night. Thus I bumped up POPs near the lakeshore. .LONG TERM...(Saturday through Wednesday) Issued at 310 PM EDT Wed Apr 4 2018 The colder than normal and somewhat snowy weather pattern should last till midweek, then a warming trend is likely. This change is based on one of those Extended East Asian Jet features coming across the Pacific and breaking through the western upper ridge next week. That should result in a more zonal flow and hence warmer temperatures. However that is in the Wed/Thu time frame. Till then winter like weather will continue thanks to cross polar flow at mid and upper levels and the upper low being displaced southward to Hudson Bay. On Saturday we have some of the coldest air yet coming into the area on northwest flow and there is enough moisture and lift for Lake Effect. So I increased the pop to likely Saturday near the lake shore. This should be good for 1 to 3 inches of snow near the lake shore and highs below freezing across the area. The Mon/Tue system still looks great. We have a Pacific shortwave that makes it through the upper ridge over the west coast and tries to merge with a northern stream wave rotating around the Hudson Bay Low. That should be good for another snow storm. Our forecast shows rain by Monday afternoon but that is due to our grids having to high of temperatures during the afternoon so really it will just mostly be snow into Tuesday morning. Some lake effect snow showers are possible Wed as cold air follows the system then warming begins. && .AVIATION...(For the 00Z TAFS through 00Z Thursday evening) Issued at 748 PM EDT Wed Apr 4 2018 VFR conditions are expected tonight and Thursday as a dry air mass settles in behind the departing system. The strato-cumulus clouds with bases of 4000-6000 ft and flurries currently overhead should mostly dissipate by 06Z. Some diurnal cumulus may reform on Thursday, but bases will be above 3000 ft. Precipitation with the next event should mostly hold off until after 00Z Thursday evening, although some MVFR cigs/vsbys could impact AZO and BTL just prior to 00Z as the snow develops/moves in. && .MARINE... Issued at 310 PM EDT Wed Apr 4 2018 The wind has fallen under gale force. Will transition this to small craft advisories. The wind continues to decrease tonight so right now Thursday is expected to feature no headlines. However by Friday...the winds and waves increase again to likely small crafts or even gales. && .HYDROLOGY... Issued at 310 PM EDT Wed Apr 4 2018 About half to three quarters of an inch of rain fell Tuesday. With near to below normal river flows for this time of year, following a drier than normal March, this beneficial rain may cause river levels to rise slightly. Flooding is not expected in the next week. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. LM...Small Craft Advisory until 4 AM EDT Thursday for LMZ844>849. && $$ UPDATE...Meade SYNOPSIS...MJS SHORT TERM...MJS LONG TERM...WDM AVIATION...Meade HYDROLOGY...CAS MARINE...MJS
Area Forecast Discussion
National Weather Service Jackson MS
914 PM CDT Wed Apr 4 2018 .UPDATE... Updated for evening discussion. && .DISCUSSION... Overnight low temperatures and frost potential were the primary focus for this forecast update. A 1025mb surface high with origins in the Canadian Yukon will continue to slide south and east through the Lower Mississippi River Valley and into eastern TN and KY by tomorrow morning. This ridge will help relax the surface pressure gradient and will supply low 30s dewpoints across a large portion of the area. Dry air, clear skies, and light to calm winds will promote efficient radiational cooling across much of the area, especially over the Golden Triangle. Have adjusted low temps down slightly along and NE of a line from Grenada to Meridian with lows dropping into the mid to low 30s. As such, areas of frost can be expected during the overnight hours for these locations and have expanded the limited risk in the HWO/graphics accordingly. Otherwise, the rest of the forecast remains on track and no other changes were needed. /TW/ Prior discussion below: Tonight through Thursday: The primary concern will be the potential for some frost over our northeast counties early Thursday morning. Latest rap and satellite imagery showed an upper flat trough over the Mississippi Valley Region. Under sunny skies breezy cool northerly winds were observed across the region with cool unseasonable readings in the 50s and 60s. A 1030 mb surface high was noted across Southern Plains. Quiet conditions can be expected for the period. With 30s dewpoints and diminishing winds under clear skies expect good radiational cooling as temps quickly drop into the 40s during the evening. With light winds lows will range from the middle 30s northeast to the upper 30s and lower 40s elsewhere. Conditions should favor some patchy frost across our northeast counties. The surface high will track toward east Tennessee by 12z Thursday. So we may not decouple completely in the low levels. For Thursday we will start to get some low level return flow under full insolation which will warm up temps toward more seasonable levels. Readings will be from the middle 60s to the lower 70s. With 30s and 40s dewpoints minimum humidity will dip into the lower to middle 20s across portions of the east. However lack of gusty winds should limit fire weather concerns. /17/ Thursday night through Tuesday: An impulse in the broad upper trough over the southern plains will move through the region Friday night into Saturday morning. With abundant warm air advection ahead of the impulse on Friday, some convection will break out early in the morning along the associated warm front which will be located in the Delta and northwards. Dewpoints will creep into the low to mid 60s during the day. There could be some strong storms with this stuff during the day as things continue to advect into and fester in the warm sector. After 00Z Saturday, a surface low looks to form in northern MS and helps to swing the cold front through the CWA. Severe weather parameters look pretty decent with 35-45 kts of bulk shear. MUCAPE up to 2000 j/kg during the day will wane at night but values up to 1000 j/kg will be plenty to keep strong storms in the area. Mid level lapse rates between 6.5 and 7 C/km are good enough to to warrant a threat of large hail too. CWAPS and helicity values are all pretty decent too. Some limiting factors are the models don`t quite line up on all of these ingredients. All of this considered though, we decided to expand the slight eastward to the Mississippi River and include the entire area in at least a marginal threat. The global models differ on the timing of the front`s exit to the east. The anafrontal precip could linger through a portion of the day on Saturday, but expect it to be east of the area by 00Z Sunday. A surface high will follow into the mid-Mississippi Valley on Sunday and quickly push east as an upper shortwave moves through the Midwest. As this system moves to our north, it will trigger showers and possibly some storms in the CWA on Monday. The system quickly tracks east and clears the area by Tuesday. An upper ridge then moves over the Mississippi Valley and leaves conditions near normal for early April in the middle of next week. /10/ && .AVIATION... 00Z TAF discussion: VFR conditions are expected through the next 24 hours as high pressure nudges into the region tonight and then starts to exit to the east during the day tomorrow. The evolution of high pressure will result in generally light north to northeast winds, transitioning to east and southeast morning through midday tomorrow, and then to southerly by tomorrow afternoon. Of course by afternoon tomorrow winds could get increase to a range of 10 to 15 mph in most areas with potential gusts up to 20 mph at GLH and GWO. Otherwise, expect high and thin clouds to increase from the west during the afternoon hours tomorrow with some patchy frost possible tomorrow at daybreak, mainly at sites GWO/GTR/CBM/NMM/MEI. /BB/ && .PRELIMINARY POINT TEMPS/POPS... Jackson 39 70 52 76 / 0 2 12 46 Meridian 33 70 49 76 / 0 2 7 25 Vicksburg 40 71 54 76 / 0 2 16 52 Hattiesburg 37 72 48 77 / 0 1 5 21 Natchez 40 72 54 77 / 0 2 9 51 Greenville 40 67 54 70 / 0 4 35 67 Greenwood 36 68 52 71 / 0 2 29 68 && .JAN WATCHES/WARNINGS/ADVISORIES... MS...None. LA...None. AR...None. && $$ TW/10/17/BB