Area Forecast Discussion
Issued by NWS Blacksburg, VA
Issued by NWS Blacksburg, VA
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895 FXUS61 KRNK 152312 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 712 PM EDT Mon Jul 15 2024 .SYNOPSIS... High pressure and unseasonably warm temperatures will cover the Mid Atlantic and southeast states tonight and Tuesday. A cold front will track out of the Ohio Valley, reaching the area late Wednesday into Thursday with showers and thunderstorms. The front, along with cooler temperatures, and a continued daily chance of precipitation will remain in the region into the weekend. && .NEAR TERM /THROUGH TUESDAY/... As of 700 PM EDT Monday... Key messages: - Heat Advisory issued for Tuesday in the piedmont of Virginia and North Carolina A few showers/storms fired over the southern Blue Ridge early this afternoon and have since diminished with only a few showers across the Mountain Empire. Anticipate showers to fade this evening. Overall should be mostly clear overnight. Patchy fog possible in the river valleys. Previous discussion from earlier this afternoon... Stratocumulus has developed over the mountains. Convective allowing models show coverage of any showers and thunderstorms as isolated. The most likely locations are in the Mountain Empire area and along the Blue Ridge south of Roanoke. Expect to see storms pop up by 4PM as the cap breaks. A majority of the precipitation will dissipate after sunset and as a shallow surface based inversion forms. Surface dew points remain mainly in the 60s overnight. Similar, to past few days, some record warm low temperatures may be be in jeopardy. Highs on Tuesday are a degree or two warmer than this afternoon. This is enough to push the max heat index to around 105 for a few hours in the afternoon. Coverage of thunderstorms Tuesday afternoon will be isolated. && .SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY NIGHT/... As of 1230 PM EDT Monday... Key Points: 1. Cold front crosses the region Wednesday into Wednesday night. 2. Locally heavy rain possible from showers and storms. 3. Cooler temperatures Thursday with values around or slightly below normal. A look at the 15 July 00Z NCEP Ensemble Mean 500 mb Geopotential heights shows a persistent upper ridge extending from western CONUS across the southern half of CONUS Wednesday and Thursday. An upper trough will be centered over the central Great Lakes and Lower Ohio Valley regions on Wednesday and the Mid-Atlantic region on Thursday. However, on Thursday, the position of this trough via the ensemble averaging becomes a bit more broad in its depiction, even trailing southwest into the mid-Mississippi Valley, also suggesting a slowing of the system. At the surface, on Tuesday night, low pressure will be centered over southern Quebec. An associated cold front will trail southwest into the Midwest. As time progresses, this front is expected to cross our region on Wednesday. Wednesday night through Thursday night, the parent low makes progress eastward as high pressure moves into the Upper Mississippi Valley/Great Lakes region. This will have result of the front over/near our region losing its forcing factor, and result in a stalling of the front over or just south of the region. Output from the 15 July 00Z Ensemble Situational Awareness Table shows 850mb temperatures falling from their high values on Tuesday to numbers closer to +18C to +21C over the area by Wednesday afternoon. While these numbers are lower, areas east of the Interstate-81 corridor will still have values that fall within the 90 to 97.5 percentile of the 30-year climatology. By Thursday afternoon, the numbers continue to decrease reaching the +16C to +18C range. Precipitable Water (PW) slowly climb Tuesday night into Wednesday with values by the afternoon ranging from 1.75 to a little over 2.00 inches across the area with the highest end of the range across southeast sections of the area. Regions with PW of 2.00 and higher will fall within the 90 to 97.5 percentile of the 30-year climatology. On Thursday, drier air will start entering the region, but result in primarily strengthening the nw-se PW gradient. Values in the far northwest are expected to be around 1.00 to 1.25 inches with values in the far southeast between 1.75 and 2.00 inches. Given the above weather pattern, very warm weather will continue through Tuesday night, with limited chances of showers and storms. Any that occur will likely be dissipating activity for a few hours in the evening from what transpires Tuesday afternoon. Additionally, towards daybreak Wednesday, there isolated coverage may occur across western sections with the approach of a cold front. This same cold front is expected to continue progressing towards, and then crossing the region sometime during the late afternoon and evening hours. Look for much better coverage of showers and storms as compared to recent days, and with PW reaching 2.00 inches for parts of the region, locally heavy rain will be possible. Thursday into Thursday night, the cold front`s parent low is expected to outpace the speed of the front, leaving an orphaned front lying somewhere across the VA/NC/SC. This feature will continue to severe as the focus for additional showers and storms through this period. With a better probability than not of the boundary being south of our region, plenty of cloud cover, and the potential for precipitation, temperatures will be notably cooler than previous days on Thursday. Confidence in the above weather scenario is moderate to high. The biggest question is just where the font takes up residency after Wednesday night and its influence on our sensible weather. && .LONG TERM /FRIDAY THROUGH MONDAY/... As of 1230 PM EDT Monday... Key Points: 1. Daily chances of showers and storms, especially southern sections. 2. Locally heavy rain possible, especially southeastern sections. 3. Around or slightly cooler than average temperatures. A look at the 15 July 00Z NCEP Ensemble Mean 500 mb Geopotential heights shows a ridge-trough-ridge blocking pattern developing across CONUS. This trough portion of this configuration is expected to be positioned from Quebec southwest into the Central Plains States. This would place our region within a persistent southwest flow aloft. At the surface, there is notable uncertainty as to the evolution of the front that arrived on Wednesday. Ensemble averaging show a nebulous area of surface high pressure to our north, and a slight weakness generally to our south. Without any strong steering flow to impact the surface features, we are expecting the front, or at least some form of remnant boundary, to remain over or near our region through Monday. Output from the 15 July 00z Ensemble Situational Awareness Table shows 850mb temperatures on Friday will average +16C to +17C across the area. For Saturday through Monday, +17C to +18C will be common. PW values on Friday will range from roughly 1.25 across northeast sections to a little over 1.75 inches the southeast. Through Monday these values and nw-se gradient change only slightly. Given the above, this portion of the forecast could provide for daily chances of showers and storms, especially over southern portions of the region, while a cold front, or its status as simply a weakening boundary, fluctuates somewhere over the region of VA/TN/NC/SC. Far southeast sections are still expected to have PW numbers close to 2.00 inches, so locally heavy rain cannot be ruled out for any day, again especially for this southeast portion of the area. We also will have to wonder about northern sections. Drier air is working its way into the Ohio Valley in association with a nearly stationary surface high. Our pattern could be one where there is an absence of precipitation across the far northern sections, with the focus closer to the VA/NC border. However, given the uncertainties is just where the remnant front will be positioned, at this time it would be unwise to suggest such a binary forecast. Our forecast will reflect a better chance of precipitation south, with lesser amounts south. Also, given the uncertainties, even for southern sections, our forecast will reflect no location with a likely, 55-74 percent, probability of precipitation. Finally, given no notable changes in the overall pattern, temperatures are expected to be around or slightly cooler than normal thanks to being on the north side of the boundary, likely abundant cloud cover, and better chances of precipitation than recent days. Confidence in the overall synoptic pattern and expected temperature trend is moderate. Confidence in the finer details of the location of the greatest coverage of precipitation is low. && .AVIATION /23Z MONDAY THROUGH SATURDAY/... As of 700 PM EDT Monday... VFR through the period. Any showers/storms will be isolated Tuesday and not enough confidence to have in tafs. Not out of the question for fog at LWB but limited threat. Average confidence for ceiling,visibility, and wind. AVIATION OUTLOOK... Better chance SHRA/TSRA chances arrive Wednesday and Thursday along with potential sub-VFR, with shower/storm chances lingering Lower confidence on location of the front and coverage of showers and thunderstorms for Friday and Saturday. && .CLIMATE... As of 700 PM EDT Monday... Roanoke reached 103 degrees this afternoon, tying the old record set back in 1936. Temperatures may come close to record high temperatures and/or record warm low temperatures for July 15 and July 16. Below you are table that list these values for locations in our region and the years those records were set. ************* RECORDS FOR July 15 ************* +=============================================+ | LOCATION | RECORD WARM LOW | Blacksburg | 72 in 1954 | Bluefield | 72 in 1942 | Danville | 79 in 1922 | Lynchburg | 77 in 1988 | Roanoke | 74 in 1995 +=============================================+ ************* RECORDS FOR July 16 ************* +=============================================+ | LOCATION | RECORD HIGH | RECORD WARM LOW | | Blacksburg | 93 in 1983 | 70 in 2020 | | Bluefield | 96 in 1988 | 71 in 1980 | | Danville | 102 in 1934 | 77 in 1920 | | Lynchburg | 103 in 1934 | 76 in 1937 | | Roanoke | 100 in 1988 | 74 in 2020 | +=============================================+ && .RNK WATCHES/WARNINGS/ADVISORIES... VA...Heat Advisory from noon to 8 PM EDT Tuesday for VAZ044>047-058- 059. NC...Heat Advisory from noon to 8 PM EDT Tuesday for NCZ006. WV...None. && $$ SYNOPSIS...AMS NEAR TERM...AMS/WP SHORT TERM...DS LONG TERM...DS AVIATION...AMS/NF/WP CLIMATE...AMS/NF/WP