Scientific Forecaster Discussion

000 fxus63 kdtx 211945 afddtx Area forecast discussion National Weather Service Detroit/Pontiac Michigan 245 PM EST Thu Feb 21 2019 Discussion... Quiet weather will continue into Friday/Friday night as large area of high pressure builds east through the area. In advance of the center of this system, expect some slight increase in cloud cover tonight over at least the northern forecast area as stratus forced by tail end of sheared vorticity lobe, enhanced by moisture flux from Lake Superior/Northern Lake Michigan, settle south into part of the night. This will complicate what would have otherwise been a decent setup for a cold night as winds become very light overnight and radiational cooling over extensive snowpack should be decent. As it is, will stick pretty close to guidance values and carry lows in the mid teens north to 20-25 south across the area. As the center of this high passes overhead on Friday, a fair amount of sun should be expected with rather light winds. This should allow temperatures to climb back into the 35-40 degree range by afternoon. Attention then turns to strong low pressure system that lifts into the region this weekend as significant upper level energy ejects northeast from the southwest Continental U.S. And eventually lifts through the northern Great Lakes. Significant jet energy dropping into upper level low spinning over Nevada will cause this system to dig into far northern Mexico on Friday. This system will then eject through the southern Rocky Mountains/plain states on into the Great Lakes over the weekend, helped along by a significant subtropical jet on the order of 150 to 175 kts. The resultant surface cyclogenesis in response to the this ejecting upper level energy is still forecast to be very aggressive dropping some 20-24 mb from Saturday into Sunday as the low center tracks from the Central Plains on through The Straits on into Ontario/Quebec. By that time, the pressure will is forecast to bottom out to 975 mb or a bit less. This system will first bring a period of rainfall, including the potential for embedded thunderstorms, as modest instability is pulled north in advance of the system as Gulf of Mexico moisture is tapped fairly efficiently as upper energy digs so far south before ejecting into the region. There is a small chance that the lead moisture will fall as a brief period of light freezing rain on Saturday. This should not be an issue as precipitation generally works south to north into the area during the afternoon with the already near 40 degrees. The more significant issue associated with this storm will be the wind potential during the day Sunday as cold air advection ensues within southwest to west flow in the wake of the passing surface low. While mixing depth may be hampered somewhat by moisture within the low level column as synoptic scale comma head wraps back into area and is enhanced by lake induced moisture flux as cold air crosses Lake Michigan, low level jet is rather close to the surface. This suggests that high end Wind Advisory criteria will quite likely be met as mixing will not have to be any deeper than 1000 feet (at most). Any mixing deeper than that brings the real possibility of the need for a High Wind Warning as 60 knot core of the low level jet is no more than 2000-4000 feet above the surface. Given the fact that these wind speeds will exist through much of the day and to some extent into the evening, suspect the risk of tree damage and/or power outages will be enhanced for this particular event. Gusty winds will continue into Monday behind the strong departing low pressure system tracking northeast into Quebec. Wind gusts of 20- 30 mph will continue to be common before the pressure gradient slackens and allows winds to decrease Monday night into Tuesday as high pressure ridges eastward across the Great Lakes. Forecast confidence decreases early/mid next week as a weak midlevel baroclinic zone attempts to set up over the region, bringing potential opportunities for light snow. Temperatures will be below normal for early to the middle of next week. && Marine... A rapidly deepening low pressure will lift from the Texas Panhandle on Saturday morning to The Straits of Mackinac by Sunday afternoon. Fresh to strong southeast wind on Saturday night will gust to near- gales at times late Saturday night. Wind is then forecast to veer to southwesterly and eventually westerly by Sunday afternoon as sustained weak to moderate gales develop over the waters. Gusts to strong gales are forecast for all marine zones with gusts to storms over the open waters of central and Northern Lake Huron. Occasional gusts to violent storm will also be possible in the vicinity of the international border during this time. Far Northern Lake Huron will be the most sensitive to small adjustments in the forecast storm track since wind within the center of the storm will be light for an extended period. Storm watches and gale watches have been issued. && Hydrology... Strong southerly flow in advance of the strong winter storm system lifting through the area will pump a warm and moist airmass into the state. Widespread rain is expected to impact Southeast Michigan late Saturday through Sunday morning with thunderstorms possible. Total rainfall amounts in excess of 0.50 inch will be possible, higher amounts for those areas impacted by thunderstorm activity. Overall flooding potential will be low. However, nuisance flooding in low lying areas will be notable given the lack of drainage due to the frozen ground. Some snow melt may also exacerbate issues in some locations. && Previous discussion... issued at 1231 PM EST Thu Feb 21 2019 Aviation... Gusty westerly wind will subside during the evening as building high pressure causes the gradient to diminish coincident with the onset of nocturnal stabilization. Paltry lake stratocu field over Southeast Michigan will not get any healthier during this time, increasing confidence in few-scattered coverage for the bulk of the period over most of the area. Integrity of cloud cover is greater over far northern lower, but the weakening gradient will limit the potential for intrusion to area taf sites overnight to no further south than mbs where a scattered group remains in place after sunset. Dtw threshold probabilities... * none && DTX watches/warnings/advisories... Michigan...none. Lake Huron...gale watch from Sunday morning through Monday afternoon for lhz462>464. Gale watch from Sunday morning through late Sunday night for lhz421- 422-441>443. Storm watch from Sunday morning through Monday afternoon for lhz361>363. Lake St Clair...gale watch from Sunday morning through late Sunday night for lcz460. Michigan waters of Lake Erie...gale watch from Sunday morning through late Sunday night for lez444. && $$ Discussion...dg/irl marine.......jvc hydrology....jvc

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