NASA - National Aeronautics and Space Administration

Forecast based on

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

Synopsis

The upper level ridge axis is centered over the Dakotas and eastern Nebraska.
By tonight, it should be centered over Ontario, Wisconsin, and Illinois.
The upper level flow is zonal from the east Pacific to the Rockies. A 100 kt
jet max is on the central coast of California. The jet is forecast to increase
by 30 kts by the end of the day. A weak surface trough extends from Nebraska
to the panhandle of Texas. No weather and few low level and mid-level clouds
are associated with this system. A shortwave exiting the Rockies is present
on the IR satellite. Thin cirrus are present over Salina. The winds have been
15-20kts since yesterday afternoon and will increase to 30 kts by this afternoon.

Prog Discussion

The NGM and ETA agree reasonably well with the placement of 500 mb ridge and
shortwaves. They do differ in the placement of the northern Plains surface low
and its intensity. The 300 mb jet has a little more eastward and northward
extent in the NGM run as compared to the ETA run.

48 hour Forecast:

12z 17 - 00Z 18 Apr: A shortwave is exiting the Rockies and will travel eastward
into the Plains. At 300 mb, difluent flow exists over northern KN, NE, and IA.
These two features should produce patchy cirrus over these state. Today should
reach 85 with the winds out of the south changing to the southwest at 30 kts.

00Z 18 Apr - 12Z 18 Apr: Another shortwave is entering the Rockies. The surface
trough will be east of Salina. The winds will become more westerly and decrease
by 10 kts. The night will have temperatures in the lower 50s and low level clouds.

12z 18 Apr - 12Z 19 Apr: The previously mentioned upstream shortwave will be ready
to exit the Rockies at 00Z Fri. A 300 mb jet nose will be over OK. Cirrus are
expected to form over the CART site in lieu of the jet nose. By 00Z Fri, the jet
be will over OK with a 140 kt jet max
entering the TX/OK panhandle. A complex surface pattern will form over KN in response
to the SW exiting the Rockies. The temperature will drop 5-10 degrees and the winds
will be out of the west at 10-15 kts.

Extended Range Discussion:

12z 19 Apr - 12Z 20 Apr: EMRF run was old. The zonal trend previously advertised
could change by Sat. 20 as both the ETA and NGM or digging a trough at 140W and
building a ridge at 120W at 500mb. A cold front should pass Fri. bringing cooler
temperatures Sat. (60's). The winds will be strong on Sat. behind the front.

Walker and Mace