Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Birmingham Alabama
949 PM CDT Friday may 22 2015
Surface high pressure centered northeast of the area has provided
an abnormally dry and cooler air mass to central Alabama.
Crossover temperatures dipped into the 40s this afternoon and
temperatures have dropped quickly after sunset in many locations.
Made some adjustments to the temperature trends. Some high clouds
and possible a few lower clouds will drift in from the west...but
with the atmosphere so dry...these clouds will not add up to much.
Went ahead and lowered overnight lows in a few spots. Fog should
not be a problem overnight.
00z taf discussion.
VFR conditions will prevail through the period with calm winds
/issued 235 PM CDT Friday may 22 2015/
Abnormally dry air in place across central Alabama today. Dewpoints
are currently in the 40s and 50s across the forecast area with
temperatures in the 70s. It doesn't get much better in central
Alabama for middle to late may. This mornings 12z bmx sounding
indicated 0.37 inches of precipitable water which is near the minimum value observed
for middle to late may. Current water vapor imagery and rap upper air
analysis indicates a closed low across the Desert Southwest with a
ridge developing across the middle-Mississippi River valley into the
northern plains. At the surface...the high pressure center is
located just to the northwest of the forecast area. For
tonight...expect the surface high will be located to the northeast
of the forecast area with the surface flow becoming more easterly.
Upper level heights will rise and expect temperatures will be a good
5 to 10 degrees warmer than last night. Radiational cooling with
mostly clear skies tonight could drop some of the sheltered
locations in the northeast down in the upper 40s with widespread 50s
The last dry day for the forecast period is expected on Saturday as
moisture values begin to creep up. The Heart of the upper level
ridge will move over the forecast area on Saturday with anti-
cyclonic flow aloft. The surface high will continue to shift to the
east and the surface winds will take on more of a southerly
component. High temperatures will also be a good 5 to 10 degrees
warmer than today with increasing heights aloft and plenty of
insolation...expect highs will top out in the 80s areawide.
The break from the warm humid typical may conditions will come to an
end on Sunday. Southerly flow at low levels will be in full force
with the surface ridge over the Atlantic. The axis of the upper
level ridge will be just to the east of the area with southwesterly
flow aloft. Precipitable water values will increase to over 1.5 inches by Sunday
afternoon. Models have been a bit more aggressive with precipitation
returning to the forecast area Sunday afternoon and have increased
probability of precipitation during the timeframe. Expect best chances will be across
western portions of the state where moisture will increase first.
The ridge to the east and trough to the west become semi-permanent
features early next week with elevated chances for showers and
storms each day. The same general trend continues throughout much of
the upcoming week with precipitable water values in the 1.5-2.0 inch range. These
values will support heavy downpours across the area each afternoon.
Due to the model consistency...have increased probability of precipitation for much of next
week into the 50-60 percent range. The NAM is the most extreme model
with 0-6km deep layer shear and SBCAPE values. From the NAM...the 0-
6km deep layer shear is around 35-45 kts with SBCAPE values around
1500-2500 j/kg on Sunday and Monday afternoons. If this were to
happen there would be a good chance for strong to marginally severe
storms each afternoon. The global models (gfs and ecmwf) are much
more tame with the severe weather parameters with the 0-6 km deep
layer shear around 20-30kts and SBCAPE 1000-2000 j/kg which is much
more typical for this time of year. For now...will side with the
global models and not mention anything in the severe weather potential statement and feature more
typical late may weather with elevated rain chances during the
afternoon. As far as any flooding threat GOES...this month has been
abnormally dry across much of the forecast area and expect any
rainfall would be beneficial.
Preliminary point temps/pops...
Gadsden 50 83 60 84 68 / 0 0 10 10 10
Anniston 53 83 63 84 69 / 0 0 10 10 10
Birmingham 56 84 67 86 70 / 0 0 10 20 10
Tuscaloosa 55 85 68 87 70 / 0 0 10 30 20
Calera 54 83 65 86 70 / 0 0 10 20 10
Auburn 56 82 63 84 68 / 0 0 10 10 10
Montgomery 57 86 67 88 70 / 0 0 10 20 20
Troy 56 85 66 87 69 / 0 0 10 20 20