Special Weather Statement, NWS New Orleans, LA

Area Forecast Discussion
National Weather Service New Orleans LA
404 AM CDT Wed May 5 2021

.SYNOPSIS...

At 3 AM CDT...outflow boundary has just about reached the Louisiana
coast. Actual cold front is just entering the northwest portion of
the CWA. Still seeing regeneration of scattered convection across
the southwest portion of the area as a shortwave is moving across
central Louisiana. Temperatures ranging from upper 60s northwest to
lower and middle 70s elsewhere.

&&

.SHORT TERM (through Friday Night)...

Based on convection allowing models, it's likely to take another 6
to 9 hours for shortwave to shift far enough south and east to push
convection far enough offshore to relax the flash flood threat
across significant population areas. Have extended the Flash
Flood Watch through 18z and mentioned potential for another 1 to
3 inches of rain. Did remove a couple forecast zones (northern
Tangipahoa and Washington Parishes) and add a couple (Upper
Terrebonne and Upper Lafourche) to the watch. Could still see some
convection over lower Plaquemines Parish beyond that, but Flash
Flood threat there would be rather limited. Another northern
stream shortwave could refire scattered convection near the
Louisiana coast Thursday before the front finally shifts far
enough offshore to eliminate any threat of precipitation by late
in the day Thursday. Drier air will be rather noticeable as
shortwave ridging to our west finally pushes into the area
Thursday night into Saturday morning.

Not sure how much temperature recovery we'll see today, will tend
below ECMWF highs. Beyond that, guidance is in fairly good
agreement through Saturday with highs upper 70s to lower 80s.
Overnight lows mainly in the 50s north half with some 60s south of
Lake Pontchartrain. 35

&&

.LONG TERM (Saturday and beyond)...

Shortwave ridging on Friday will gradually break down as a trough
over the West Coast moves eastward. Flow will be zonal by Sunday.
Airmass will be pretty dry on Friday, but as onshore flow gets re-
established on Saturday, moisture will increase. The upper level low
over eastern Canada will gradually pull a frontal boundary into the
area by about Monday. As impulses move through the zonal flow across
the area, we'll likely see a few rounds of convection from Sunday
onward into midweek. Current blended solutions are considerably
closer to the 12z ECMWF solution than they are the GFS, which was
relatively dry. After a couple days of drying, likely to pour more
rain into the area early next week. Timing of individual impulses
at this time range is questionable, and expect later forecasts
will raise PoPs in some periods and lower in others.

Comfortable temperatures for Friday and Saturday with lower
humidity. May need to trend overnight lows down a bit across the
eastern half of the area in favorable drainage locations like the
Pearl and Pascagoula River basins. Daytime highs should probably fit
just below the drier GFS highs for Monday and Tuesday. 35

&&

.AVIATION...

Most terminals not being impacted directly by convection are seeing
VFR ceilings at this time. Main exception is KBTR, where MVFR
ceilings are occurring near frontal boundary. Threat of TSRA will
likely impact all but KBTR and KMCB through the morning hours, and
amendments will handle this as necessary. Do expect MVFR ceilings to
predominate for much of the daytime hours as cumulus/stratocumulus
develops outside of convection. Ceilings will eventually improve to
VFR overnight. If winds decouple toward sunrise on Thursday,
wouldn't be surprised to see some patchy fog develop. 35

&&

.MARINE...

Main threat over the next 24-48 hours for marine interests will be
the potential for thunderstorms. As boundary finally shifts
offshore, cool dry air advection will allow winds to increase
somewhat over the open waters, and may be brief periods where winds
increase to around 15 knots, but not anticipating need for headlines
at this time. When winds return to an onshore component over the
weekend, there may be a need for Small Craft Exercise Caution or
Advisory headlines Saturday night or Sunday, especially over the
western waters.

&&

.PRELIMINARY POINT TEMPS/POPS...
MCB  78  57  79  54 /  10   0   0   0
BTR  80  60  82  57 /  20   0   0   0
ASD  80  61  83  57 /  70  10   0   0
MSY  80  68  83  65 /  80  10  10   0
GPT  80  63  82  59 /  80  10   0   0
PQL  80  62  82  56 /  80  10  10   0

&&

.LIX WATCHES/WARNINGS/ADVISORIES...
LA...Flash Flood Watch until 1 PM CDT this afternoon for LAZ046-049-
     050-056>061-063>065-072-075>078.

GM...None.

MS...Flash Flood Watch until 1 PM CDT this afternoon for MSZ077-
     080>082.

GM...None.

&&

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Special Weather Statement
National Weather Service New Orleans LA
514 AM CDT Wed May 5 2021

MSZ081-082-051100-
Jackson-Harrison-
514 AM CDT Wed May 5 2021

...A LINE OF STRONG THUNDERSTORMS WILL AFFECT HARRISON AND WESTERN
JACKSON COUNTIES...

At 513 AM CDT, radar indicated strong thunderstorms were located
along a line extending from 6 miles west of Lyman to near Long Beach
to 7 miles east of Bay St. Louis. Movement was east at 35 mph.

Winds in excess of 30 mph and pea size hail are possible with these
storms.

Locations impacted include...
Gulfport, Biloxi, Ocean Springs, Long Beach, St. Martin, D'iberville,
Latimer, Lyman, Gulf Hills, Vancleave, Gulf Park Estates, Hickory
Hills, Saucier and Gulfport Airport.

This includes the following Interstates...
 Interstate 10 in Mississippi between mile markers 23 and 61.
 Interstate 110 in Mississippi between mile markers 3 and 4.

Frequent cloud to ground lightning is occurring with this storm.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

These storms may intensify, so be certain to monitor local radio
stations and available television stations for additional information
and possible warnings from the National Weather Service.

LAT...LON 3034 8870 3037 8885 3038 8885 3038 8878
      3043 8885 3042 8901 3040 8886 3038 8907
      3030 8928 3038 8926 3054 8934 3067 8889
      3074 8880 3074 8872 3053 8861
TIME...MOT...LOC 1013Z 254DEG 30KT 3050 8924 3040 8919 3030 8922