textproduct: Raleigh

WHAT HAS CHANGED

As of 255 PM Tuesday...

* Slight rise in minimum temperatures for Wednesday morning, although a hard freeze still appears likely.

KEY MESSAGES

As of 255 PM Tuesday...

1) A hard freeze is likely for most locations in the forecast area tonight into Wednesday morning with much below normal temperatures for the middle of March.

2) A backdoor front is expected to move into and through NC from the north sometime between late Sun and early Tue, but differences in timing among the models is large, which means a low-confidence temperature and rain chance forecast Sun-Tue.

DISCUSSION

As of 255 PM Tuesday...

KEY MESSAGE 1... A hard freeze is likely for most locations in the forecast area tonight into Wednesday morning with much below normal temperatures for the middle of March.

High pressure is currently centered over Louisiana, which will expand to the northeast over the next 24 hours. Diurnal cumulus is currently expanding east from the Triad towards the I-95 corridor. The cloud cover will increase through the afternoon and decrease this evening. After the diurnal cu fades away, high clouds will overspread the region after midnight. The trickiest part when it comes to the temperature forecast tonight will be how much radiational cooling is able to occur between the afternoon cumulus and the overnight cirrus. The wind is not expected to go calm overnight, although the wind should be at or below 5 kt. The forecast on this cycle has risen back one or two degrees because the wind is not expected to go calm in addition to greater cloud cover. Even with the slight increase in the temperature forecast, this still calls for a forecast in the 20s in all locations. Although the growing season has not officially begun, any early budding plants/vegetation will likely experience a hard freeze if not protected.

KEY MESSAGE 2... A backdoor front is expected to move into and through NC from the north sometime between late Sun and early Tue, but differences in timing among the models is large, which means a low-confidence temperature and rain chance forecast Sun-Tue.

The strong mid level ridge over the Desert Southwest and NW Mexico much of this week will weaken a bit and flatten as it spreads eastward, resulting in trend to above-normal to much-above-normal temps for NC Fri into Sun, as we stay in a WNW flat and dry-source steering flow. Then, a frigid polar low over the Arctic and N Canada will dig southward into S Canada and the N CONUS, with emerging significant differences among deterministic models and ensemble members and means regarding the timing and amplitude of this resultant broad trough spreading and digging over the Great Lakes and Northeast early next week. These model differences become especially stark and important Sun night into Tue, when the associated surface backdoor front is expected to push southward into and through NC, with the very warm air south of it quickly supplanted by a frigid surface high building in from the N and a potential transient CAD event toward the middle of next week. The model differences are most stark and important Sun night into Tue, when the NBM and LREF spread between the 10th and 90th percentiles reaches an astonishing 35-40 degrees F, depending on when the front pushes through (and, to a lesser degree, the amount of clouds and precip at any given time), with the AIGEFS-ens similar with a 25-35 degrees F spread. The westerly mid level trajectory component and the E-to-W surface ridge to our south, across the Gulf/FL/Bahamas (limiting Gulf moisture influx), would tend to favor light QPF with any frontal precip, so will maintain low to no pops for now. But be aware that higher pops may be needed in this period in later forecasts. And while our forecast temps will reflect a mild scenario with lows in the 50s Sun night and highs in the upper 60s to low 70s Mon, confidence is very low, and these readings could easily be 10- 20 degrees higher or lower than these values. Stay tuned.

AVIATION /00Z WEDNESDAY THROUGH SUNDAY/

As of 800 PM Tuesday...

TAF period: VFR conditions are expected with high confidence through 00z/Thursday. Gusty winds this evening will become light and variable overnight through Wednesday.

Outlook: VFR conditions are forecast into the weekend.

RAH WATCHES/WARNINGS/ADVISORIES

None.