Forecast based on

• on satellite
• current surface observations
• 00 UTC ETA
• 00 UTC NGM
• 09 UTC MAPS/RUC
• MRF
• 12z ECWMF

Synopsis

Thin cirrus and persistent contrails are already presentnt over
Salina. The upper level ridge axis at 500 and 300 mb is just west of Kansas
and Oklahoma. The surface high which built in the midwest yesterday will
move to the southeast as a strong surface low moves from the Pacific north-
west into the northern Plains and Alberta/Saskatchewan. The surface pressure
gradient will gradually increase throughout the day resulting in southerly
to southwesterly winds of 15-20 kts by the late afternoon. The day should
be sunny with thickening cirrus as the day progresses. The IR satellite
imagery shows cirrus spilling over the ridge axis into Kansas and Oklahoma.

Prog Discussion

The NGM, ETA, and AVN handle the speed of the Pacific
northwest shortwave and placement of the northern Plains surface low differ-
ently. We have gone with the slower ETA solution which keeps the surface
trough west of the forecast area and schedules the frontal passages to
occur after 00z Thu 18. All models show the upper level pattern to become
zonal by 00z Thu 18. The MRF shows the zonal pattern to persist, and it
does not change until 00z Mon 22.

48 hour Forecast:

12z 16 - 00Z 17 Apr: An upper level ridge is centered over the eastern
Rockies. The ridge will flatten as a strong Pacific northwest shortwave moves
through it. The winds will gradually increase throughout the day as the
surface gradient increases in the northern and central Plains in response
to a surface low progressing out of the Pacific northwest into Alberta/Sas-
ketchewan. The day should be clear with increasing cirrus clouds. The temp-
erature will rise into the upper 70's.

00Z 17 Apr - 12Z 17 Apr: A Pacific shortwave moves on shore. The 500 mb ridge
axis is now centered over MN, IO, and MO. At the surface, a front is analyzed
over TX/OK pandhandle and western Kansas. The warm southerly flow will keep
the temperatures in the 50's.

12z 17 Apr - 12Z 18 Apr: The upper level flow will become zonal and a 120 kt
jet is analyzed on the west coast at 35N. A cold frontal passage is progged
for late Wed. night/early Thur. morning (LST). Ahead of the front, there is a
slight chance of scattered thunderstorms if moisture advects from the south.
The winds will remain strong (20-25 kts, gusts to 30 kts) and southernly. The
temperatures will be in the upper 70's and lower 80's. High level clouds will
persist.

Extended Range Discussion:

12z 18 Apr - 12Z 19 Apr: After the cold frontal passage, the daytime tempera-
tures will drop by 10-15oF, and the winds will become northernly. The upper
level flow pattern will be zonal at 500 and 300 mb, with the polar jet centered
over southern CA and AZ.

Walker and Mace