textproduct: Raleigh

WHAT HAS CHANGED

As of 800 PM Wednesday...

* Increased Fire Danger criteria (within 5 mph wind and 5% RH of critical thresholds) will likely be met for all of cntl NC on Thu.

KEY MESSAGES

As of 325 PM Wednesday...

1) Dry fuels combined with lower humidity and near record heat will promote fire weather concerns through the weekend.

2) An early-season heat wave will result in near record high temperatures through Saturday.

3) A late-weekend pattern transition is expected with a cold frontal passage. Low-end rain chances are expected on Sunday, followed by much cooler temperatures early next week.

DISCUSSION

As of 325 PM Wednesday...

KEY MESSAGE 1... Dry fuels combined with lower humidity and near record heat will promote fire weather concerns through the weekend.

The anomalous mid-level ridge will amplify along the eastern seaboard through the end of the week. Associated subsidence over the southeast will promote continued dry conditions at least through Saturday. Precipitation as a percentage of normal over the past 30 days is as low as 5 to 25% for portions of our area worsening the elevated drought conditions. As such, fuels have been anomalously dry for some time.

Deep mixing on Thursday will promote a bit gustier sfc flow upwards of 20 kts or so in the afternoon. PWAT will remain below an inch, and given deep mixing, expect afternoon relative humidity to bottom out in the mid to upper 20s. While the combined expected min RH and max gusts will be sub IFD criteria, the aforementioned fire risk due to anomalously dry fuels has prompted a request for another IFD for our entire CWA on Thursday (to be issued by the evening shift). A few CAMs are hinting at late night isolated showers possibly reaching the western/central Piedmont. However, limited moisture would only allow for trace to maybe a few hundreds of an inch of rain, if any at all.

Winds will be lighter on Friday and Saturday but dry conditions will persist. As such, expect Increased Fire Danger Statements to likely be issued daily until things change significantly.

Light rain will be possible Sunday, but QPF should be generally pretty low. As such, fire weather concerns will likely persist late weekend (isolated lightning on Sunday would be concerning) into early next week.

KEY MESSAGE 2... An early-season heat wave will result in near record high temperatures through Saturday.

Anomalously strong subtropical ridging will persist over the Southeast US for much of the period from now through Saturday, other than a brief mainly dry shortwave passage on Friday. At the surface, a Bermuda High will bring warm SW flow to central NC. 1000-850 mb thicknesses are modeled to be around the 95th percentile for this time of year, and with plenty of sunshine, forecast maximum and minimum temperatures get close to or reach record highs each day.

Mostly lower-90s for highs and lower-to-mid-60s for lows are expected from Thursday through Saturday, which is around 15-20 degrees above normal. Friday may be slightly cooler, particularly across the north where forecast highs are in the mid-to-upper-80s. This will depend on the degree of cloudiness and very light precipitation chances from the passage of a shortwave trough, which looks to have a surface reflection that briefly turns the low-level flow more WNW. Can't rule out some mid-90s on Saturday, which based on low-level thicknesses looks to be the hottest day. For reference, this would get close to the hottest temperatures ever recorded any day in the month of April. See the climate section below for more details.

Fortunately, humidity looks tolerable, with dew points mostly bottoming out in the lower-to-mid-50s each day, perhaps even some 40s especially in the west. So heat indices will be about 2-4 degrees cooler than the actual air temperatures each day. Still, several days in a row of highs in the lower-90s could result in heat stress for sensitive individuals and those working and exercising outdoors.

KEY MESSAGE 3... A late-weekend pattern transition is expected with a cold frontal passage. Low-end rain chances are expected on Sunday, followed by much cooler temperatures early next week.

A broad mid/upper trough will advance into the Eastern US from the Plains this weekend. An associated cold front will move across central NC, which could produce some isolated to scattered showers from Saturday night into Sunday. While there is still a lot of uncertainty on timing of the frontal passage, the latest GFS and ECMWF and most of their ensembles have sped up, bringing it through in the morning which would give very little time for surface heating and instability to occur. This combined with the best forcing and moisture from the trough focused to our north mean rainfall amounts look light, with ensemble means less than two tenths of an inch. So expect very little if any relief from the drought.

It will turn significantly cooler early next week with highs in the mid-60s to 70 on Monday and lower-to-mid-70s on Tuesday. Sunday and Monday nights will be chilly with lows mostly in the upper-30s to lower-40s. Isolated mid-30s are on the table according to statistical guidance, particularly on Monday night which looks to have the best radiational cooling potential. So will need to watch for the threat of patchy frost.

AVIATION /00Z THURSDAY THROUGH MONDAY

As of 800 PM Wednesday...

Sub-tropical high pressure and dry air extending across the South Atlantic states will favor a high probability of VFR conditions and sswly surface winds that will strengthen and become gusty to 20-25 kts with afternoon heating on Thursday.

Outlook: A relatively strong mid-level trough will move across cntl NC with associated rain/showers and ceilings as low as 6-8 thousand ft Fri morning. Another chance of (probably VFR) rain will exist along and behind a cold front that will move across cntl NC early Sunday.

CLIMATE

All-Time Records for April:

KGSO: 95 on 4/28/1915 KRDU: 95 on 4/23/1980 and 4/28/1896 KFAY: 96 on 4/12/1930

Record High Temperatures:

April 15: KGSO: 90/2006 KRDU: 92/1941 KFAY: 95/2006

April 16: KGSO: 88/2002 KRDU: 92/1941 KFAY: 94/2006

April 17: KGSO: 90/1967 KRDU: 93/1896 KFAY: 92/1941

April 18: KGSO: 90/1976 KRDU: 95/1896 KFAY: 93/1941

Record High Minimum Temperatures:

April 15: KRDU: 64/1993

April 16: KGSO: 66/2006 KRDU: 64/1912

April 17: KGSO: 63/2002 KRDU: 67/1896 KFAY: 66/1921

April 18: KGSO: 66/1909 KRDU: 63/1941 KFAY: 67/2002

RAH WATCHES/WARNINGS/ADVISORIES

None.