Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Memphis Tennessee
620 am CDT Friday may 22 2015
updated to add 12z aviation discussion.
Previous discussion... /issued 325 am CDT Friday may 22 2015/
Canadian high pressure over the middle south this morning has
resulted in clear skies...calm winds...and temperatures that are
15 to 20 degrees below normal. High pressure will move east today
with a return of southeasterly low level flow. Dry conditions will
continue with a warm up in temperatures back into the lower and
middle 70s....which are still about 10 degrees below normal.
Upper level ridging should remain in place across the forecast
area into Saturday with southerly flow bringing a slow increase in
low level humidity levels and temperatures returning back to
seasonal normals in the lower 80s.
The pattern will shift by the end of the weekend as an upper level
low pressure system digs across the southwestern U.S. And results
in developing southwesterly flow aloft. This will increase deep
moisture across the region and allow for increasing chances for
showers and thunderstorms by Sunday as a shortwave lifts northeast
from the arklatex. The highest chances for showers and
thunderstorms Sunday should remain along and west of the
Mississippi River. A few of these storms could produce heavy
rainfall as precipitable water values surge to near 2 inches and
dewpoints rise to near 70 degrees in these locales by Sunday
afternoon. A few stronger storms with gusty winds may also occur
as moderate instability develops with sbcapes in excess of 1500
j/kg and deep layer shear increases to greater than 40 kts. Weak
lapse rates and a deeply moist airmass should temper any more
significant severe weather threat.
A wet weather pattern will continue through the first half of next
week as a series of shortwave disturbances interact with a very
moist airmass in place over the region. Deep tropical moist
connection from the tropical east Pacific and western Gulf of
Mexico should set the stage for heavy rainfall potential.
Widespread showers and thunderstorms are expected for Monday
through Wednesday...especially along and east of the Mississippi
River. An increased flash flood threat may develop early next
week and flash flood/flood watches may be needed during this time
period. This will be monitored by later forecasts through the
weekend. Plan to add this potential flood threat to the latest
hazardous weather outlook. Temperatures early next week may be
held down some by the enhanced rainfall and cloud cover.
The pattern should become slightly less amplified by the second
half of next week but with continued southwesterly flow aloft.
The moist airmass should remain in place but with less synoptic
forcing. This should lead to a mainly diurnally focused
convective pattern with storms mainly developing during peak
heating. The atmosphere should become increasingly
thermodynamically unstable and may support a more favorable late
Spring/early Summer wet microburst pattern. Temperatures should
warm back to near seasonal averages for the second half of next
week with high humidity levels remaining in place.
12z taf cycle
Patchy fog may reduce visibilities down to MVFR/IFR conditions
this morning at mkl. Otherwise...VFR conditions expected to
prevail at sites through the period. NE/east winds between 6-10 kts
will become light after 23/00z.