Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 201010 AFDRAH AREA FORECAST DISCUSSION National Weather Service Raleigh NC 610 AM EDT Fri Sep 20 2019 .SYNOPSIS... Canadian high pressure will build southward across the southern middle Atlantic states through tonight, then offshore this weekend. && .NEAR TERM /THROUGH TONIGHT/... As of 325 AM Friday... A subtropical ridge centered over the Mid-South this morning will strengthen and expand ewd across the sern US through tonight. Underlying surface high pressure centered at 07Z over RIC will consequently remain anchored across the srn middle Atlantic and Carolinas. Stratocumulus should be more limited in coverage today versus Thu owing to a veering of the 925 mb flow to a wly/offshore component. Temperatures will moderate slightly but remain below average, with highs in the upr 70s to around 80 degrees and lows, with strong radiational cooling once again, in the upr 40s to mid 50s. && .SHORT TERM /SATURDAY THROUGH SATURDAY NIGHT/... As of 335 AM Friday... There will be little change (from the previous 24 hrs) in the synoptic pattern at the surface and aloft across cntl NC. That pattern will be characterized by continued surface ridging across NC, though with a developing Appalachian-lee trough with diurnal heating, and a 592-593 dm/322-323 dm subtropical ridge remaining over the sern US at 500 and 700 mb, respectively. The presence and influence of the subsident subtropical ridge, and otherwise modification of the antecedent cP airmass, will yield warmer/above average temperatures mostly in the lwr-mid 80s. Low temperatures are likely to remain below average, however, given both radiational cooling potential in the presence of the surface ridge and the foregoing cP dryness and contribution to a large diurnal range, with lows mostly in the mid-upr 50s. && .LONG TERM /SUNDAY THROUGH THURSDAY/... As of 415 AM Friday... Mostly dry weather and warming conditions can be expected through the extended with a slight cool down occurring on Tuesday due to a frontal passage. By the end of the extended period though models have come into remarkable agreement that a anomalously strong ridge will begin to take shape across the southeastern United States with temperatures rising well above normal towards the end of the next work week. The extended will open up with a weak sub- tropical ridge located across the southern United States and an upper level low heading east over the Midwestern United States. Low level thicknesses will continue to rise Sunday towards 1400 m putting high temperatures in the mid to upper 80s. The forecast will remain dry Sunday as PWATs stay around 1.00", or slightly below normal for this time of year. Monday night into Tuesday morning the upper level low that was over the Midwestern United States Sunday will be crossing the Great Lakes region. A weak cold front will then attempt to cross the zones Tuesday morning before getting hung up across central NC. The ECMWF and GFS are fairly similar here and stall the front near RDU. The chances of precipitation with the front still looks rather paltry here as forecast soundings show multiple layers of remnant dry air from the prior air mass. Latest GFS soundings are slightly more robust with moisture, as saturation in the column now exists from ~750 to 600 mb. The primary 500 mb height rise/fall couplet is well off to the north though with lift coming in the form of only weak PVA. All of the above means that the forecast looks dry Monday into Tuesday. By Wednesday afternoon whatever is left of the stalled baroclinic zone will loose cohesion allowing warm moist air to surge north. Thursday afternoon mid-level ridging will begin to take shape across the southeastern United States as heights collapse over the Pacific Northwest. 1000/ 850 mb thicknesses on Thursday are forecast to surge towards ~1430m with highs in the 90s across the Coastal Plain. && .AVIATION /10Z FRIDAY THROUGH TUESDAY/... As of 610 AM Friday... Under the influence of Canadian high pressure, mainly VFR conditions are expected through tonight. However, shallow and localized radiation fog will be likely again after 06Z mainly at RWI. Otherwise, surface winds will be light and variable as the center of the Canadian high builds overhead, with very little cloud coverage. Outlook: The continued presence of Canadian high pressure will maintain mainly VFR conditions in cntl NC for the next several days. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...MWS NEAR TERM...MWS SHORT TERM...MWS LONG TERM...Haines AVIATION...MWS is the U.S. government's official web portal to all federal, state and local government web resources and services.