textproduct: Raleigh

SYNOPSIS

Arctic high pressure centered over the Carolinas today will slowly shift off the coast on Tuesday and Wednesday. A warm front will lift north across the region on Thursday. A cold front will sweep across the area late Thursday and Friday.

NEAR TERM /THROUGH TONIGHT/

As of 140 AM Monday...

* Cold Weather Advisory will expire by 9am this morning.

* Continued very cold today with daytime highs in the lower to mid 30s which is 15 to 20 degrees below normal.

A strong and cold 1038 mb Arctic high pressure system centered across the OH Valley early this morning will shift southeast and weaken as it moves across the Carolinas today and becomes centered across the Carolina coast tonight. Gusty northwesterly winds across the area on Sunday and Sunday night have relaxed considerably early this morning. Wind chill values as of 1am generally ranged between 5 and 10 degrees. Despite temperatures that will drop a few more degrees overnight, wind chill values may moderate a touch as the winds relax. Prefer to keep the current messaging and will keep the Cold Weather Advisory in effect despite explicit values that will creep above criteria toward daybreak.

Low level thickness values in the 1550s this morning will support cold highs today in the lower to mid 30s despite lots of sunshine and no snow cover. These highs are between 15 and 20 degrees below average. Expect good radiational conditions tonight and we've adjusted the low temperatures downward into the upper teens in most locations. There are signals for a few patches of high cirrus clouds tonight with the potential for some orographic enhancement although the availability of high- level moisture is limited and the lack of an inversion around 850-700 is inconsistent with the conceptual model. -Blaes

SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/

As of 230 AM Monday...

After a cold Tuesday morning, as the surface high moves east and offshore, S/SW return flow will bring milder temperatures to central NC in the afternoon, though still slightly below normal. Forecast highs are in the mid-to-upper-40s and forecast lows in the mid-20s to 30. Other than some possible lingering orographic cirrus in the morning over the far northern Piedmont, skies will be sunny.

LONG TERM /WEDNESDAY THROUGH SUNDAY/

As of 330 AM Monday...

The warming trend will continue from Wednesday through Thursday night as temperatures turn above normal with strengthening S/SW flow. Wednesday's forecast highs are mid-to-upper-50s and lows in the 30s. Thursday's forecast highs are upper-50s to mid-60s and lows in the upper-30s to 50. A weakening shortwave may move through on Wednesday evening/night, but any precipitation should dissipate as it crosses the Mountains and the only effect here will be a deck of mid and high clouds.

Confidence continues to increase for the Thursday/Thursday night event, but overall impacts look limited. A chance of light stratiform rain arrives on Thursday morning and afternoon as a warm front lifts north through the area. Any amounts would be around a tenth of an inch or less, and POPs are only in the 20-30% chance range. A better chance of precipitation comes on Thursday night as a vigorous shortwave and associated surface low lift NE from the Upper Great Lakes into southern Ontario and Quebec. This will drag a cold front that crosses central NC late Thursday night and early Friday morning, with a plume of anomalous PW values 200+% of normal out ahead of it. The ECMWF and GFS continue to have good agreement on timing, and the GFS has trended toward the ECMWF in showing a more amplified trough, with a majority of their ensemble members depicting precipitation during this period. So POPs on Thursday night have increased further to likely areawide, and total expected rainfall amounts have increased, although they are still limited to a quarter to half inch on average (highest NW) by the fast movement and strongest mid-level height falls occurring to our north. Can't rule out isolated thunder in the Sandhills and Coastal Plain, but models depict only 100-200 J/kg of CAPE at most given the timing is overnight and 60+ degree dew points stay to our SE.

Friday and Saturday's temperatures will drop back closer to normal, with highs in the 50s and lows Friday night in the mid-20s to 30. Post-frontal gustiness on Friday could reach 20-30 mph based on momentum transfer from GFS BUFKIT soundings. The next cold front looks to move through on Sunday night, but it is weaker and drier, with only a small minority of ensemble members depicting precipitation. So only have slight chance POPs at this time. Temperatures ahead of the front on Sunday will be warmer, with highs in the 60s and lows in the mid-30s to lower-40s.

AVIATION /18Z MONDAY THROUGH SATURDAY/

As of 1155 AM Monday...

VFR conditions are highly likely over the next 24 hours at central NC terminals, with few to no clouds, as only some high cloudiness is expected across the northern Piedmont (INT/GSO/RDU) 08z-13z late tonight/early Tue morning. Surface winds will be light at 8 kts or less from the N and NW today then from the S and SW Tue. While winds aloft tonight may not strictly meet the low level wind shear criterion of being within a 200 ft depth, with a deep nearly isothermal layer in the lowest several thousand ft AGL, potential wind speed stratification in the vertical may still result in some mechanical turbulence 03z-10z, particularly for small aircraft.

Looking beyond 18z Tue, VFR conditions are likely to hold through Wed. The risk for sub-VFR conditions increases Wed night and remains high through early Fri morning, with a chance of rain. LLWS may occur at INT/GSO Wed night as well. VFR conditions should return Fri, lasting into Sat, but strong gusty winds from the NW are possible on Fri. -GIH

RAH WATCHES/WARNINGS/ADVISORIES

None.