Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 271136 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 736 AM EDT WED JUL 27 2016 .SYNOPSIS... High pressure will expand across the Carolinas, maintaining uncomfortable levels of heat and humidity this week. Isolated to scattered showers and thunderstorms are possible each afternoon and evening. The chances increase heading into early next week. && .NEAR TERM /THROUGH TONIGHT/... As of 635 AM Wednesday...Will go with a persistence type forecast, using yesterday as the model day to work off of. Near term models such as the Hi-Res WRF, the HRRR, and the RAP all indicate a repeat of yesterday with only isolated convection possible along the sea breeze...and just north of the ILM CWA running from RAH to MHX CWAs. The outlier of those 3 models is the hi-res WRF where it paints a possible cluster of storms along the ILM to FAY line. At this point it seems too far south given the strength of the upper ridge and the strength of the convective lid and continued warm temps in the low and mid levels. Of note for the ILM NC CWA, various model sounding data indicate 500 mb temps slightly decrease to between -3 to -4.5 degrees C this aftn and evening...and the subsidence inversion is not as strong or prevalent. Again, this is mainly for the ILM NC portions. As mentioned b4, will continue with persistence from yesterday and not jump on the WRF bandwagon to increase POPs as of yet. For max temps, stayed closer to the GFS Mos guidance and for lows, stayed closer to the NAM Mos guidance. This based on the latest verification for the ILM CWA. The mid and upper 90s for Highs combined with low to mid 70s dewpoints yield heat indices in the 105 to 109 degree range. Even after the sea breeze pushes thru, temps may drop to around 90 but dewpoints will increase to the upper 70s. This will not improve the Heat indices, in fact, it may actually make them worse. The Heat Advisory will run from 11 AM to 7 PM today. && .SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... As of 415 AM Wednesday...Ridging aloft and at the sfc will dominate once again the ILM CWA this period with the beginnings of this ridge breaking down late Friday. The upper ridging and warm temps aloft will again limit lapse rates and maintain a convective lid across the fa this period, with weaknesses in this lid occurring by fri. Models indicate some decrease in progged 500mb temps to -5 degrees C or a degree lower by late Fri. However, the GFS still indicates some remaining decent subsidence aloft and associated inversion during Fri. Overall, will highlight a low chance POP across the entire ILM CWA on Fri, not just along and ahead of the sea breeze which is highlighted on Thursday. Heat advisories will be needed for both Thu and Fri. There is a remote possibility that Heat Indices could breach Excessive Heat Warning criteria, which are Heat indices 110 degrees or higher. For daily max temps, stayed closer to the GFS Mos guidance. And for daily Min temps, stayed closer to the NAM Mos guidance. This is a carry over from the Near term forecast with the reasoning remaining the same. Each day during the late evening thru pre-dawn hours, a low level SW to WSW 20 to 30 kt jet will occur. This will keep a well mixed sfc layer, in turn keeping fog development to a minimum, if any. && .LONG TERM /SATURDAY THROUGH TUESDAY/... As of 415 AM Wednesday...Mid level heights will fall very slowly through the period allowing and along with an increase in PWs, chance of convection will increase. Profiles for Saturday are still somewhat unfavorable although there is plenty of moisture. Mid level cooling along with similar moisture profiles increases chances Sunday through Tuesday. We go from slight chance to just under likely by Monday which continues through Tuesday. Regarding temperatures, I really don`t see much in the way of cold air advection in the lower levels but more convection should shave a couple degrees off the middle and upper 90s we are seeing now. && .AVIATION /12Z WEDNESDAY THROUGH SUNDAY/...
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As of 12Z...VFR this TAF valid period. SW-WSW winds will back to the S-SW by afternoon, earlier at the coastal terminals. Highest speeds of 15-20 KT during the afternoon at the coastal terminals. Isolated aftn/evng convection is possible mainly north of the terminals along an old outflow boundary, and near KLBT along the NC portion of the Piedmont trough. Any activity that is able to develop will move east in the mid-level flow and stay N of the terminals, but will monitor in case activity develops further S. Chances are low attm that any of this activity will affect KILM/KLBT, but have added VCSH to the KILM terminal 17-19Z associated with the sea breeze. Winds will slowly veer TO SW-WSW and decrease later in the evening. EXTENDED OUTLOOK...Isolated to scattered afternoon convection through Sunday may create brief periods of MVFR/IFR. Otherwise expect VFR.
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&& .MARINE... NEAR TERM /THROUGH TONIGHT/... As of 635 AM Wednesday...Early this morning, the low level SW jet will keep the SW winds busy across the ILM local waters. By daylight mid-morning, these winds will slightly diminish to 10 to 15 kt. This afternoon thru mid-evening...the sea breeze will provide an increase in winds near shore, with SSW at 15 kt with gusts to 20 kt. The winds late this evening and overnight will transition away from the sea breeze...to another low level jet episode with sw winds mixing down to the ocean sfc. Significant seas will basically run in the 2 to 4 foot range with locally produced wind driven waves at 3 to 6 second periods dominating the overall seas. Convection coverage, if any, will be isolated at best. SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... As of 415 AM Wednesday...The ridging from the sfc high will be suppressed southward. This will increase the westerly component in the wind directions during this period. The sfc pg will also tighten slightly as a result of the ridge axis oriented further south. in addition, the Carolinas sfc trof, aka the Piedmont trof, will orient itself across the Central and western portions of the Carolinas this period. This will produce some tightening of the sfc pg across the area waters this period. The daily inland progression of the sea breeze may be limited due to the increase in the westerly component of the winds...and their speeds during this period. A daily nocturnal low level jet will again occur during the late Thu evening through the pre-dawn hrs of Friday. However, models indicate this will not be the case Friday night and early Saturday. Overall wind speeds will run in the 10 to 20 kt range with the 20 kt mainly in the form of gusts. Significant seas will run 2 to 4 ft and possibly 3 to 5 ft late Thursday Night thru early Friday. If the latter occurs, then a SCEC may be needed. Convection will again be limited, with the best possibility occurring late Friday. LONG TERM /SATURDAY THROUGH SUNDAY/... As of 415 AM Wednesday...Bermuda high pressure along with the inland Piedmont trough will be the main drivers of winds and seas for the coastal waters. A south to southwest flow of 10-15 knots will prevail with significant seas of 1-3 feet. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...Heat Advisory from 11 AM this morning to 7 PM EDT this evening for SCZ017-023-024-032-033-039-053>056. NC...Heat Advisory from 11 AM this morning to 7 PM EDT this evening for NCZ087-096-099-105>110. MARINE...None. && $$ SYNOPSIS...SHK NEAR TERM...DCH SHORT TERM...DCH LONG TERM...SHK AVIATION...MRR

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