579 FXUS64 KBMX 101850 AFDBMX Area Forecast Discussion National Weather Service Birmingham AL 150 PM CDT Wed Jun 10 2020 .UPDATE... Afternoon Update. && .SHORT TERM... /Updated at 0147 PM CDT Wed Jun 10 2020/ Through Thursday. It was a messy start to the day for some of us across Central AL. The areal coverage of showers and a couple thunderstorms overperformed hi-res modeling this morning over eastern portions of the forecast area due to the decaying MCS/boundary which moved into our western counties. Despite this, temperatures have only risen about a degree or two slower than expected, and breaks in the clouds should still allow most areas to reach their forecast highs. Subsident air has taken hold behind the boundary while dry mid-level air has begun to push into the state. This has allowed for clearing conditions in the west/northwest. As a result, I removed afternoon PoPs for areas generally west of a line from Jefferson to Marengo counties. The frontal boundary has begun to reach the AL/MS state line with surface winds weakly veering and dewpoints dropping in the Lower MS Valley as the parent trough moves into the Ohio Valley. East of I-65, abundant moisture is still present with a low deck of scattered to broken clouds while latest mesoanalysis indicates surface destabilization ~3000-3500 J/kg. We're beginning to see a few storms firing, primarily in our southeast, with building cloud tops noted on vis satellite imagery. As dry air continues to stream into the mid-levels, there will be increasing support for a few thunderstorms capable of strong, damaging winds in these areas. Based on latest trends, will make adjustments to the Marginal Risk area & timing, with the main threat focused on our southeast through this afternoon before declining in tune with the loss of daytime heating and the eastward progression of the front. Stable conditions return tonight as the front moves east of the forecast area. A northerly, dry flow will provide lower humidity, and slightly lower temperatures for tomorrow. Look for highs in the lower 80s north to upper 80s south under sunny skies. 86 Previous short-term discussion: /Updated at 0310 AM CDT Wed Jun 10 2020/ This morning and afternoon. A decaying MCS can be observed moving eastward across Mississippi this morning, and as of ~3 AM has exhibited a forward speed that is outrunning the synoptic dry line/cold front that originally initiated the system near the ArkLaTex yesterday. As such, a theta-e boundary/cold pool feature will race eastward into Central AL later this morning and may establish near the Black Warrior River basin around Noon - the synoptic boundary should catch up shortly thereafter. Either way, a noticeably drier airmass remains behind the synoptic boundary with a broad reservoir of deep tropical moisture still in place across much of the Southeast (mid 70s dewpoints & PWs 1.8-2.0"). This, and afternoon heat, will foster another day of numerous showers and thunderstorms. I placed PoPs more generously along and southeast of I-20/59 today, along & east of the forecast surface boundary/theta-e gradient. Compared to yesterday, much of today's thermodynamic environment remains generally the same (We'll get a better picture of this after the 12z RAOB). Temperatures aloft cooled a couple degrees after Cristobal moved out of the region, though mid-level lapse rates are progged to remain ~6 C/km. This will temper updraft strength a bit, though temperatures in the upper 80s to near 90 and dewpoints in the mid 70s still support 3,000-4,000 J/kg SBCAPE and SB LIs around -8. Thus, strong thunderstorms are possible once initiation occurs downstream of the synoptic boundary & convective temperatures are approached, as well as weak upper-level diffluence helping to aid in overall forcing. Effective bulk shear is forecast to increase to 20- 30 kts during this time as winds aloft increase a tad with the strong shortwave ejecting across the Ohio Valley. This will exacerbate thunderstorm impacts as cold pools aggregate later in the afternoon, potentially creating damaging/severe wind gusts. Earlier in the convective life cycle, discrete cells will need to be watched as well as DCAPE values could run 900-1,300 J/kg in places, as suggested by drier air spreading across the Deep South on mid-level WV imagery. This suggests dry air entrainment and resultant strong downbursts/microbursts (this can be seen in areas where the microburst composite parameter increases to values of 3-5+ on RAP mesoanalysis). Severe criteria hail is not expected as temps aloft still remain a little warm, though good CAPE values and marginal shear suggest stronger updrafts could produce small hail stones on occasion. All things considered, the severe/HWO forecast remains on track overall. Best chances remain across the eastern two-thirds of Central AL during the afternoon and early evening. Activity generally wanes once the lower troposphere stabilizes this evening and the synoptic front moves west to east. Of note: lightning safety should also be taken seriously today. Tonight through Thursday afternoon. As the drier, stable airmass settles across Central AL later tonight, rain chances decrease with a noticeably drier feel to the air. Dewpoints are 15-20 degrees F lower behind this boundary. Winds will continue to veer with time as overnight temperatures fall into into the upper 60s northwest, to upper 60s in the southeast. Thursday will feature northerly flow, mostly sunny skies, and no mentionable rain chances. We'll still see 80s for highs in the afternoon, though heat indices will be much more tolerable overall. 40/Sizemore .LONG TERM... /Updated at 1213 PM CDT Wed Jun 10 2020/ A few small updates to the long term forecast. A large deepening ridge will begin to build further south tomorrow which will bring clearing skies and somewhat lower dewpoints. The mainly clear, rain-free days are expected for much of the period, however, an upper low is expected to develop across the Mid-Atlantic region introducing a slight chance of showers and thunderstorms by the first and middle of next week. Any chance of rain will likely remain across the eastern-third of the state. 17/KLAWS Previous long-term discussion: /Updated at 0310 AM CDT Wed Jun 10 2020/ Thursday night through Tuesday. Drier weather with mild temperatures expected for most of Central AL over the weekend. High pressure builds in quickly behind the departing frontal boundary Thursday night into Friday. Dewpoints drop into the 50s to low 60s, which will allow for overnight low temps to reach into the low 60s as well. The frontal boundary becomes stationary just to our south, stretching all the way up the East Coast. Synoptically, a trough deepens across the Pacific Coast as an upper level low slide southward out of the Gulf of Alaska. This will amplify the ridging across the Rockies and Central Plains and allow the trough over the Great Lakes to dip southward. For us, this likely won't cause any significant changes to the sensible weather except for a small chance that some showers build back in across our southeastern counties Saturday afternoon with the increase forcing along the stationary front. An upper level low begins to develop over the Great Lakes region on Sunday, then quickly becomes cut off from the flow regime. It's at this point that model guidance continues to struggle, which isn't surprising. The GFS drops the cut-off low southward through the Appalachians and into the Tidewater Region Monday through Tuesday, while the ECMWF lags the cut-off low back over the Ohio Valley. This difference in placement will determine whether Central AL sees any influence from the upper low (synoptic lifting) or not. Without any substantial moisture return, it may be difficult for any showers to develop even if we do see the increased lift from the low. Given the inconsistency in the models and the drier antecedent conditions, I'll maintain only minimal PoPs (5-10%) Sunday through Tuesday. 25/Owen && .AVIATION... 18Z TAF Discussion. A frontal passage will produce active weather across the eastern and southern terminals for the first half of this period followed by drying conditions overnight into tomorrow. Ceilings have begun to rise due to afternoon mixing which will allow VFR conditions to return at all sites. Currently, the front is moving into eastern Mississippi with most of the activity found well ahead of the boundary. Therefore, the greatest chance for a scattered shower or thunderstorm and associated impacts to flight criteria will primarily exist for our eastern and southern terminals, especially MGM and TOI where a greater amount of destabilization has begun to occur under scattered to broken skies. Winds may become gusty as the front moves through with a few gusts up to 20-25 kts. Clearing conditions and rising ceilings will occur late tonight behind the front with winds shifting from southwesterly to north- northwesterly. Favorable aviation weather will be in place tomorrow under mostly sunny skies. 86 && .FIRE WEATHER... A cold front moves through today, bringing another shot of thunderstorms and a shift from the southerly flow to more northerly flow. After the front moves out late tonight, drier weather builds in and will continue through the rest of the week. Min RHs will remain in the 40% range Thursday before dropping into the 30% range Friday and Saturday. && .PRELIMINARY POINT TEMPS/POPS... Gadsden 61 84 60 86 61 / 30 0 0 0 0 Anniston 61 84 60 86 61 / 40 0 0 0 0 Birmingham 63 85 63 87 64 / 20 0 0 0 0 Tuscaloosa 63 85 62 87 63 / 10 0 0 0 0 Calera 62 84 62 86 63 / 30 0 0 0 0 Auburn 65 86 63 86 65 / 50 0 0 0 0 Montgomery 64 87 63 89 66 / 50 0 0 0 0 Troy 67 88 64 89 67 / 50 0 0 0 0 && .BMX WATCHES/WARNINGS/ADVISORIES/... None. && $$