... System brings rain with a higher elevation wintry mix Friday into Saturday. A stronger wave crosses Sunday, followed by a cold front Sunday night.
NEAR TERM /THROUGH TONIGHT/... As of 915 AM Friday...
Made some slight adjustments to sky cover over the next few hours to better represent current satellite. There are a few holes in cloud cover this morning but clouds are slowly filling back into the area from the west as the morning progresses. Overall, current forecast remains on track.
As of 620 AM Friday...
Clearing worked a bit farther south than originally anticipated this morning. Updated sky and temperature grids to reflect better clearing/radiational cooling across the Metro Valley. Otherwise, forecast on track.
As of 230 AM Friday...
Mid and upper level cloudiness associated with H300 150KT jet streak overhead early this morning will briefly thin out, especially across the northern half of the area by daybreak as this feature exits to the east. Tried to reflect a quick dip in the hourly temperatures heading into daybreak where this occurs.
Will see mid/upper level cloudiness surge back into the region by midday ahead of an approaching southern stream wave. Low level southerly flow strengthens in response with warm, moist air surging into the region by late this afternoon. This should yield a quick warm-up into the upper 40s/lower 50s for most of the lower elevations through early this afternoon. Strong low level warm air advection will work in concert with a weak midlevel disturbance to generate widespread light precipitation across much of the forecast area late this afternoon and evening. For most of the lower elevations this will likely remain rain through the end of precipitation with amounts generally under half an inch for the south and southeast down to around a tenth of an inch across our north. With these amounts, minimal hydro impacts are expected for the near term. For the mountains and locations favored for cold air damming, forecast certainty is lower with a decent spread in both the strength/position of the warm nose and strength of cold air damming discriminating between rain/freezing rain/sleet/snow. Overall, think CAD along with cooler high elevation temperatures will be sufficiently cold for wintry precipitation and warm nose will be sufficient for partial and then complete melting of hydrometeors. This yield a rain or snow to sleet or freezing rain mix for most locations inside the winter weather advisory by this evening before flow turning more southwesterly into daybreak brings a transition to all rain as the next disturbance arrives. Total ice accumulations of up to a tenth of an inch are expected in the advisory area with up to 3-4 inches of snow along the highest mountain ridges.
Mainly light easterly winds this morning increase out of the southeast through midday. Gusts of 25-30 mph will be common in the warm wedge this afternoon/evening where higher momentum air associated with aforementioned low level warm surge isentropically descends to the surface in the lee of impinged terrain. Elsewhere, gusts mainly limited to 20 mph or less.
SHORT TERM /SATURDAY THROUGH MONDAY/... As of 335 AM Friday...
Wave after wave brings copious rainfall this period which, together with the wet antecedent conditions, spells some potential for flooding.
The first in a series of waves will be ongoing Saturday morning across mainly southeast portions of the forecast area. Temperatures and dew points climb just above freezing by the start of the period, 12Z Saturday, along the highest ridges and eastern slopes, as the last of the cold air is eroded there by moderately strong low level south to southwest flow.
Moisture flux and forcing maximize across southeast portions of the forecast area, where PW values climb to around an inch, rainfall totals could approach that over a roughly 12-hour period ending midday Saturday.
Weak ridging builds into the middle Ohio Valley Saturday, and the rain will gradually decrease from northwest to southeast, resulting in a brief lull Saturday afternoon and evening, especially north.
The next wave approaches Saturday night, and then crosses Sunday morning. This wave is progged to be stronger and more amplified, and the axis of heavier rainfall sets up farther north compared to its predecessor, a key factor in the hydrologic assessment this weekend. The model envelop for the axis of heaviest rainfall with this wave ranges from central to northwest portions of the forecast area, with an h85 50 kt feed cranking PW values to 1.25 inches or better.
Skinny elevated CAPE can develop along and just south of the axis of the axis of heaviest moisture, where h85 theta e gets to 320K or better with dew points approaching 10C at that level. Thus have added the slight chance for thunder Saturday night through Sunday across mainly central and southeastern portions of the forecast area.
A cold front crosses the area from northwest to southeast Sunday afternoon and night, generally pushing the rain to the south and east. However, one last wave along that cold front may bring one last round of heavy rainfall across southern portions of the forecast area Sunday night. This may be enough to kick streams over the edge.
The storm total QPF for today through Sunday night is close to central guidance, and reflects amounts ranging from close to an inch northwest to over three inches across southeast portions of the area, although some models depict a distinct northern maxima over northern or central portions of the area, with amounts of two to in some cases three inches or better. This could lead to excessive rainfall by Sunday, especially given saturated conditions and strong stream and river flow coming out of the recent winter weather stretch.
Very dry air brings stout clearing from northwest to southeast on Monday.
Temperatures close to central guidance, except a bit higher south of the front on Sunday.
LONG TERM /MONDAY NIGHT THROUGH THURSDAY/... As of 335 AM Friday...
A moisture-starved secondary cold front crosses Monday night, followed by arctic high pressure Tuesday morning. This brings dry weather Monday night and Tuesday, but with a cold morning.
Once high pressure exits Tuesday night, models are at odds with systems affecting the area during the middle and latter portions of the upcoming work week, as we seem to be getting into the season of southern stream closed off lows. Some models are stronger and more organized with the first system, while others emphasize the second system more. The forecast reflects the chance for precipitation with either system, mainly rain, although some snow or mixed wintry precipitation is possible in the mountains. The northern stream and colder air may eventually become involved with the second system at the end of the work week.
Dropped lows in the valleys Tuesday morning beneath the clear, calm environment of arctic high pressure as long as it arrives in time. Otherwise, central guidance was generally accepted.