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Area Forecast Discussion
Issued by NWS Blacksburg, VA
Issued by NWS Blacksburg, VA
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814 FXUS61 KRNK 281043 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 643 AM EDT Fri Jun 28 2024 .SYNOPSIS... High pressure will track across the mid-Atlantic states today, then shift northeast off the New England coast Saturday. A frontal boundary to our south will keep moisture around into Saturday, with chances for showers and storms. Another front moves in from the northwest Sunday. && .NEAR TERM /THROUGH TONIGHT/... As of 130 AM EDT Friday... Key Messages: 1) Upslope scattered showers/few storms through Friday night. 2) Less humid today but increasing again Friday night. There is a low level theta-e ridge strung across the Blue Ridge this morning with low level convergence. This has resulted in isolated showers. Slow movers but weak and models are fading this out through the early morning but would not be surprised for a pop up shower to form at times. For today, southeast flow will increase as high pressure works across the mid-Atlantic, while a front stays situated from the coast of NC into the Gulf Coast states. Seems as we head through the morning, dewpoints will start to drop across western and northern sections of our forecast area (WV through the central VA piedmont), but could keep higher RH across southside VA into NC closer to the front. Models are varying on convection today, and leaned toward a blend of the Hi-RES ARW/FV3, which will have chance pops situated across the NC mountains and foothills northward to the souther Blue Ridge and Mountain Empire of SW VA, this afternoon, with less to no coverage northeast of a Lewisburg to Danville line. Confidence is high that storms will be limited as instability seems lacking but enough heating could produce a few storms, but nothing severe. Showers and storms will be slow movers so some heavy rainfall appears likely but most will see little or no rain. Tonight, expect a lull in the evening but moisture starts to ramp up again after midnight, that will see widely scattered showers over most of the mountains/foothills, with 20 to 30 percent chance of getting any measurable rainfall, with slightly higher chances again over the NC mountains/foothills northeast along the Blue Ridge into Patrick/Carroll counties in VA. Highs to will be close to normal as we have a mix of sun and clouds with more clouds across the Blue Ridge and either side. Temps will range from the mid 80s to near 90 east of the Blue Ridge, to upper 70s to mid 80s west. Tonight, as dewpoints rise and cloud cover starts to increase, thinking lows will be on the warm/muggy side with upper 60s to around 70 for most of the region. Forecast confidence is high on temperatures and winds, and average on sky cover and shower/storm coverage. && .SHORT TERM /SATURDAY THROUGH MONDAY NIGHT/... As of 100 AM EDT Friday... Key Points: 1. Well above normal temperatures Saturday and Sunday. 2. Showers and storms Saturday and Sunday, some with locally heavy rain and strong/damaging winds. 3. Drier and cooler for Monday. A look at the 27 June 12Z NCEP Ensemble Mean 500 mb Geopotential heights shows an upper level trough over the Upper Mississippi River Valley on Saturday morning, with southwest flow across our region. As we progress into Sunday and Monday, this trough is expected to be over the Great Lakes Sunday morning and just east of our region Monday morning. By Monday night, the trough will be centered over the Canadian Maritimes with ridging building into the Ohio Valley. At the surface on Saturday morning, low pressure is expected to be over Michigan with a southwest trailing cold front into MO/KS/OK/AR. By Sunday morning, this front is expected to be over our region. High pressure will be nosing into the region from the west Monday morning, and be centered overhead by late Monday night. Output from the 27 June 12Z Ensemble Situational Awareness Table shows 850mb temperatures on Saturday around +16C to +18C over the region and +18C to +20C for Sunday. For sections of the region the upper end of these ranges correspond to the 90 to 97.5 percentile of the 30-year climatology. For Monday, values drop notably reaching the +12C to +14C range over the area, with the low end of this range within the 2.5 to 10 percentile of climatology. Precipitable water values for Saturday are expected to be very high for this time of year with numbers around 2.00 inches. This places the western half of the region higher than the 99.5 percentile of the 30-year climatology and the eastern half with a range in the 97.5 to 99.5 percentile. This swath of extraordinary high values sweeps across the region Saturday night immediately in advance of the a cold front. On Sunday, drier values work their way into the region by the afternoon, but values in the forenoon, especially in the southeast sections, will remain very high. Sunday night into Monday night, precipitable water values are expected to continue to fall. Values of 0.50 to 0.75 inch are expected by Monday into Monday night, or values within the 2.5 to 10 percentile of the 30-year climatology. The above weather scenario offers a Saturday with very good probabilities of showers and storms that contain moderate to heavy rainfall. Temperatures are expected to be well above normal. Additionally, The Day-3 Severe Thunderstorm Outlook from SPC offers Marginal Risk of severe weather generally for areas along and west of the Interstate-81 corridor. Damaging winds would be the greatest threat. On Sunday, while well above normal temperatures continue, the details are not as clear on the precipitation timing. However, a cold front looks to arrive early and then lingers over eastern parts of the region through mid-day and/or the passage of the 850mb cold front helps to maintain showers and storms across mainly eastern parts of the region. By Sunday night, cooler and drier air is expected to be entering the region with this pattern continuing into Monday night. Confidence in the above weather forecast is moderate to high. && .LONG TERM /TUESDAY THROUGH THURSDAY/... As of 100 AM EDT Friday... Key Points: 1. Temperatures and humidity trending higher each day. 2. Chance of showers/storms late Wednesday night into Thursday. A look at the 27 June 12Z NCEP Ensemble Mean 500 mb Geopotential heights shows a building upper ridge over the Southeast US. Nearly zonal flow is expected near the US/Canadian border. The exception is a shortwave trough that is expected to progress from the Dakotas on Thursday morning to Upper Mississippi Valley by late Thursday night. At the surface on Tuesday morning, high pressure will be centered over the area. By Wednesday morning, the high will start shifting east of the region as a cold front approaches through the Ohio Valley. By Thursday morning, the cold front will be over or near our region. Output from the 27 June 12Z Ensemble Situational Awareness Table shows 850mb temperatures around +16C for Tuesday, +19C to +21C for Wednesday, +20C to +22C on Thursday. The upper end of the range on Wednesday falls within the 90 to 99 percentile of the 30-year climatology. On Thursday, much of the area is expected to be within the 97.5 to 99 percentile of climatology with potentially the mountains of North Carolina higher than the 99 percentile. For precipitable water values on Tuesday, expected numbers around or just shy of 1.00 inch. Values climb on Wednesday to around 1.50 inch. For Thursday, numbers climb more to 1.75 to 2.00 inches, or within the 90 to 97.5 percentile of the 30-year climatology. The above weather scenario offers a period of rebuilding heat and humidity after the cooler and drier Monday. Temperatures should trend higher each day. Primarily dry conditions are expected until late Wednesday night and Thursday with the approach/arrival of a cold front and the airmass in advance of it trending progressively unstable. Confidence in the above weather forecast is moderate to high. && .AVIATION /12Z FRIDAY THROUGH TUESDAY/... As of 150 AM EDT Friday... High probability for VFR for terminals through the period. Some MVFR ceilings are possible at BLF/BCB/ROA if showers move across but coverage today looks limited more toward the NC mountains, south of ROA/BCB/BLF. Overall anticipate SKC/SCT clouds this morning, then scattered to broken in the 4-8kft range today into this evening, with again possible 2-3kft cigs along the Blue Ridge south of ROA/BCB. Winds will be light this morning then turning east to southeast today and increasing to 8-12kts especially west of the Blue Ridge. Cannot rule out a few gusts to 20kts around BLF. Ceilings will lower to MVFR possibly IFR after 07z at most sites. A few showers possible but too low chance to have in the tafs. EXTENDED AVIATION OUTLOOK... A greater coverage of thunderstorms and associated MVFR flight conditions is expected Saturday and Sunday, but VFR outside of any storms. Monday-Tuesday appears to be VFR as high pressure works in from the north. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...VFJ/WP NEAR TERM...WP SHORT TERM...DS LONG TERM...DS AVIATION...RCS/WP