708 FXUS64 KHUN 072315 AFDHUN Area Forecast Discussion National Weather Service Huntsville AL 615 PM CDT Fri Oct 7 2022 ...New AVIATION... .NEAR TERM... (Remainder of today and tonight) Issued at 247 PM CDT Fri Oct 7 2022 Amplification of a broad longwave trough across central/eastern North America will continue this afternoon, as a progressive shortwave trough currently dropping into the Lower Great Lakes region begins to lift northeastward into New England. As this occurs, a fairly cold/dry airmass of Canadian origin building southward through the northern Plains will spread southward into the region, although this airmass will likely not arrive in the local area until late this evening/early Saturday morning. Thus, after a warm afternoon with highs in the u70s-l80s, strengthening low-level cold advection through persistent northerly flow around 10 MPH will drive temperatures down into the 40s for most of the area by sunrise, with lows ranging from the lower 40s in our TN counties to the upper 40s across southern Cullman County. && .SHORT TERM... (Saturday through Sunday night) Issued at 247 PM CDT Fri Oct 7 2022 Latest short term model consensus suggests that the longwave trough noted above will be reinforced over the course of the weekend, as an upper low predicted to dig southeastward across Hudson Bay overnight opens into a trough and travels cyclonically through southern Ontario and into the Canadian maritime provinces by the end of the short term period. Our forecast area will remain along the southern edge of stronger mid-level cyclonic flow to our north, with this expected to result in sunny/dry conditions tomorrow and highs ranging from l-m 60s in elevated terrain to the u60s-l70s in the valley. Although northerly winds will remain rather brisk during the morning hours, the pressure gradient will relax by late Saturday afternoon as a surface ridge builds eastward into the TN/OH Valleys, and remains centered to our immediate north/east through Monday morning. The combination of light-calm flow in the boundary layer and dewpoints in the l-m 30s will be favorable for radiational cooling both Saturday and Sunday night, with a patchy-areal coverage of frost possible during the morning hours, particularly across our TN zones and in far northeast AL. However, one potential negative factor regarding frost development at least on Saturday night could be an increase in high-level cloudiness associated with a mid-level vort max crossing the Ozarks/Mid-South region. && .LONG TERM... (Monday through Friday) Issued at 247 PM CDT Fri Oct 7 2022 Global models suggest that a change in the synoptic flow pattern will begin early next week, as a low-amplitude ridge at the 500-mb level translates eastward across the southern CONUS in response to deepening northern stream trough digging across the Canadian Rockies. Present indications are that the ridge axis aloft will shift to the east of the region by Monday night, allowing west- southwesterly flow to resume by Tuesday morning. Although guidance indicates that the west-southwesterly flow will steadily strengthen through the mid-week period as the height gradient contracts between the trough to our northwest and a subtropical high to our southeast, it will not be until Tuesday when low- level return flow becomes sufficient to result in a notable increase in boundary layer moisture. Chances for showers will begin to increase early Wednesday morning, as both deep-layer moisture advection and synoptic scale ascent increase in the strengthening warm advection regime downstream from the amplifying trough to our northwest, with a few thunderstorms possible by by Wednesday afternoon as dewpoints rise into the u50s-l60s in the warm sector airmass ahead of the related surface cold front. This regime will become even more robust during the period from Wednesday night-Thursday morning, as the south-southwesterly low-level jet increases to 35-45 knots and PWAT values rise into the 1.6-1.8 inch range, setting the stage for a fairly widespread coverage of showers and thunderstorms in what could be our first Autumn severe convective event. A cooler and drier airmass of North Pacific origin will spread into the region in the wake of the front, with pleasant weather conditions returning by the end of the work week. && .AVIATION... (00Z TAFS) Issued at 615 PM CDT Fri Oct 7 2022 Even with the passage of a dry cold front, VFR conds are generally expected thru the TAF period. Mid/high clouds filtering into the area from the west will also linger into much of Sat. Light/var winds will become north around 10kt with higher gusts Sat morning as well. && .HUN WATCHES/WARNINGS/ADVISORIES... AL...None. TN...None. && $$ NEAR TERM...70 SHORT TERM....70 LONG TERM....70 AVIATION...09