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fxus64 kjan 271054 
afdjan

Area forecast discussion
National Weather Service Jackson MS
554 am CDT Thu Jul 27 2017

Update...
updated for 12z aviation discussion

&&

Aviation...
12z taf discussion:
VFR conditions are expected throughout the taf period. A cold
front will begin to approach the northern sites towards the end of
the period slightly increasing the chances for showers and
thunderstorms. However, the best chances of showers/storms will
be beyond the range of this period.

&&

Discussion...
today through tonight...

Dangerous heat and accompanying humidity will pose a threat to the
arklamiss today. A broad, steep, and stagnant upper ridge centered
over the Western Plains will continue to slowly build eastward into
the arklamiss as the day continues resulting in 500 mb heights
increasing to around 593dm. 850 temps will once again reach levels
just above 20 deg c throughout the region. High temperatures on
yesterday ranged from 94-97 degrees areawide and all indications
support a 1-2 degree increase areawide today. Models were aggressive
with dewpoints mixing down today, especially in the eastern portions
of the region where temperatures will near triple digits. Dewpoints
were adjusted to dampen the aggressive mixing scenario. This
resulted in increased forecasted Max heat indices over eastern
portions of Mississippi, thus the heat advisory was expanded
eastward. Expect heat index values to range from 105-109 throughout
most of the arklamiss except in the Pinebelt region where heat
indices will range from 100-104. Moisture will begin to increase
overnight ahead of an approaching cold front. The increasing
moisture and cloud cover will lead to a warm, muggy night.
Temperatures will only fall to the upper to mid 70's in the Delta
and the mid to lower 70's elsewhere. There is still some uncertainty
with the timing of the passage and precipitation associated with it,
however precip is expected to hold off until Friday morning. /Jpm3/

Friday through next Wednesday night,

The greatest weather impacts are expected during early portions of
the long range period, particularly from Friday into Saturday when
hot and humid conditions are expected to combine with a strong cold
front to bring the potential for a few rounds of storms capable of
producing marginal severe weather and localized flooding. The first
round of storms may approach northern portions of the arklamiss and
the Highway 82 corridor by daybreak Friday as a decaying convective
system moves into the forecast area. The effects of the morning
convection on subsequent convective development are unclear with
guidance showing a multitude of possibilities, but it does appear
at least that temperatures and heat stress will be reduced over
northern portions of the forecast area and have adjusted the
severe weather potential statement/graphic to account for this.

For now, have followed along with the idea that the early Friday
morning convection will dissipate in time to allow for renewed
convective development during peak heating over northern portions
of the area, but the greatest potential for very moist and
unstable air and severe weather/heavy rain potential may be
along/south of the I-20 corridor from late afternoon into Friday
evening. The threat for any intense convection should become more
confined Saturday to southern portions of the area where several
cams and model ensembles suggest another convective system may
move through, but this is highly conditional on prior convective
evolution, so confidence is quite low concerning the severe
weather/heavy rain threats for Saturday. Overall the primary
change to the previous severe weather potential statement/graphics was to distinguish the
threats for Friday and Saturday more.

Looking ahead, the strong front will push through the arklamiss
by Saturday night as an amplified upper level pattern and deep
trough become established over the eastern Continental U.S. Resulting in dry
northerly flow and unseasonably low relative humidity values from
Sunday through early in the week. As we go into the middle of next
week, the airmass should modify with greater moisture resulting
in increased diurnal convective precipitation coverage. /Ec/

&&

Preliminary point temps/pops...
Jackson 96 74 93 74 / 5 4 28 47
Meridian 97 73 92 73 / 9 3 32 55
Vicksburg 95 74 92 73 / 4 4 28 46
Hattiesburg 95 73 94 75 / 12 3 20 48
Natchez 93 73 90 74 / 5 3 23 46
Greenville 95 77 90 72 / 4 15 49 43
Greenwood 95 76 89 72 / 4 12 48 44

&&

Jan watches/warnings/advisories...
MS...heat advisory until 8 PM CDT this evening for msz028>033-037>039-
043>046-048>063.

Heat advisory until 8 PM CDT this evening for msz018-019-025>027-
034>036-040>042-047.

La...heat advisory until 8 PM CDT this evening for laz026.

Heat advisory until 8 PM CDT this evening for laz007>009-015-016-
023>025.

Arkansas...heat advisory until 8 PM CDT this evening for arz074-075.



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