897 FXUS64 KHUN 071258 AFDHUN Area Forecast Discussion National Weather Service Huntsville AL 658 AM CST Thu Mar 7 2019 .NEAR TERM...(Today) Issued at 445 AM CST Thu Mar 7 2019 West-northwest flow aloft will continue to subside across the region today, as a deamplifying mid-level ridge translates across the Plains and into the MS Valley. Although a few weak disturbances aloft will bring periods of enhanced mid and high-level cloud cover, we expect conditions to remain dry, with perhaps some virga beginning to overspread the western portion of the forecast area close to sunset this evening. At the surface, a ridge centered across the southern Appalachians continues to provide light/variable flow at the surface, with temperatures currently in the l-m 20s for most of the region. However, as the ridge shifts further eastward, light southeasterly return flow will begin and temps should rise above freezing for most locations by 8 AM CST, at which time we plan to let the current Freeze Warning expire. Highs today will reach the u40s-l50s. .SHORT TERM...(Tonight through Saturday night) Issued at 445 AM CST Thu Mar 7 2019 A shortwave trough currently lifting northeastward into western SD/NE is predicted to round the apex of the deamplifying ridge, reaching the MO Valley by 08/00Z and the lower Great Lakes by 12Z, while gradually phasing with another disturbance to its southwest. During this same period, a low related to the trailing mid-level disturbance will spread east-southeastward through the southern Plains Red River Valley, with a warm front expected to become established across northern TN by early Friday morning. Strengthening low-level warm/moist advection across our region will support a fairly rapid increase in shower activity after Midnight, with mid- level lapse rates also supportive of the development of a few deeper convective elements closer to sunrise. To our northwest, models still suggest that forcing for ascent associated with the synoptic trough over the mid-MS Valley region will initiate a cluster of more widespread elevated convection across northeastern AR/western TN, which will build southeastward into the CWFA after 08/12Z as the trough shifts eastward and steering flow veers to northwest. At this point in the day, convection should still be slightly elevated, and will likely pose threats from only lightning and locally heavy rainfall. Additional showers/storms may develop later in the afternoon, in the vicinity of the effective frontal boundary, which may drift back southward in response to diabatic cooling processes. By Friday evening, we expect a mid-level ridge (downstream from a stronger vort max ejecting northeastward over the southwestern CONUS) to translate eastward across the local area, with winds aloft backing to the southwest and increasing after Midnight. Although all global models suggest that a wave embedded in the southwest flow aloft will lift northeastward over the region early Saturday morning, lift from this feature may not be realized due to the development of a mid-level inversion noted in some forecast soundings. If the inversion does not develop or is weaker than predicted, then widespread convection will likely materialize before sunrise Saturday morning. However, at this point we have kept POPs in the 60-70% range, as even weak lift in the nearly saturated boundary layer should foster the development of numerous showers. The vort max ejecting over the southwestern CONUS on Friday night is predicted to deepen and assume a sharp negative tilt as it lifts northeastward across the central Plains and into the western Great Lakes Sunday morning. With the strongest synoptic scale ascent related to this trough expected to bypass our region to the north, precipitation on Saturday will be driven by intense lower tropospheric warm/moist air advection. Given the prospects for widespread rain and thunderstorms early in the day, we have much uncertainty regarding the potential for a round of severe convection later Saturday afternoon/evening as a weak cold front drifts southward. However, with MLCAPE potentially as high as 500-1000 J/kg, we feel the slight risk area denoted by SPC is certainly warranted, as the southwesterly low-level jet will peak in the 45-55 knot range during the afternoon/evening. Of more concern is the potential for widespread/locally heavy rainfall, and with anticipated storm total amounts ranging from 1.75-2.50 inches, we could certainly see an increase in areal/river flooding once again. .LONG TERM...(Sunday through Wednesday) Issued at 445 AM CST Thu Mar 7 2019 The long term seems to be a rinse and repeat of the short term starting out with dry conditions for a few days before returning to an unsettled pattern. On the bright side, if you were not a fan of the chilly temps recently, temps will be near normal or slightly above through the extended. On Sunday, the cold front will be south of us but if it gets hung up as the ECMWF suggests, a few showers may linger across the southern tier of counties. There will not be a significant temp change behind this front as temps will still be above normal during the day on Sunday with highs in the upper 60s with the difference being felt Sunday night as lows will be in the lower 40s about 10 degrees cooler than Saturday night. A sfc high in the N Plains/Midwest will build southeastward as we head into Monday, however a weak disturbance will slide through zonal flow aloft returning a slight chance for showers to start the work week. Looking to stay dry on Tuesday as the axis of the upper level ridge moves overhead. Daytime highs will be in the lower 60s and overnight lows will only reach the lower 50s as southerly flow increases through the night due to the increasing pressure gradient ahead of our next system. Dry conditions do not last long as this next system digs across the Desert SW and into the Plains by Tuesday night/Wednesday, developing a sfc low in the Southern Plains. This will bring southwesterly flow aloft as it pushes the ridge over to the East Coast. Models are in fair agreement up to this point with the ridge and sfc high lingering across eastern seaboard, the upper-level trough and sfc low are forced to sharply lift NE and drag a cold front into the MS Valley on Wednesday. Southerly sfc winds will increase to ~10-15mph with higher gusts and linger into the night. Combined with the increased SW flow aloft, temps will reach the upper 60s and a plentiful amount of moisture will stream into the region. Models disagree on the strength, exact track and the timing of this system. The GFS has precip ahead of the front reaching the TN Valley Wednesday afternoon as the system lifts into the N Plains/N MS Valley. The ECMWF has a slightly stronger but slower system with a tad further track. Regardless, showers and thunderstorms will develop along and ahead of the cold front and spread into the TN Valley on Wednesday. Greatest coverage is on Wednesday night into Thursday when sfc waves and a LLJ increase lift increasing the potential for heavy rainfall and thunderstorm coverage. It will be slow to move out of the forecast area as a northern wind shift does not occur until Friday, finally giving it a push to the southeast. Forecast soundings have PWATs reaching ~1.5" (99th percentile) with some instability and a fair amount of shear. Combined with the possibility that this could bring a few inches of rainfall (storm total of Tuesday night through Thursday) on top of what we receive this weekend this system will be monitored so stay tuned to the forecast for additional updates. && .AVIATION...(For the 06Z TAFS through 06Z Thursday night) Issued at 1116 PM CST Wed Mar 6 2019 VFR weather should continue across the central Tennessee Valley into late Thu evening. Surface high pressure over the region will produce light/variable winds overnight. A stream of cirrus originating from the tropical Pacific should remain south of the area, thus scattered mid and high clouds are expected. Winds shortly after daybreak should become SE-S, then increase into the 5-10kt range by the late morning and continue into the late afternoon. Winds should back more to the SE Thu evening, with somewhat lower clouds arriving from the west. && .HUN WATCHES/WARNINGS/ADVISORIES... AL...Freeze Warning until 8 AM CST this morning for ALZ001>010-016. TN...Freeze Warning until 8 AM CST this morning for TNZ076-096-097. && $$ NEAR TERM...70/DD SHORT TERM...70/DD LONG TERM...JMS AVIATION...RSB For more information please visit our website at weather.gov/huntsville.