This weekend Philip Forecast

Current Conditions:

A highly amplified pattern is currently in place across the CONUS in the upper levels. A large trough is currently located over the eastern United States with a large ridge axis centered over the Dakotas. Moisture brought into the Rockies from Tropical Storm Edouard is enhancing thunderstorm development beneath a region of upper-level diffluence in the four-corners region into Wyoming. A potent 500 mb low is currently situated just off the northwest coast. At the surface, southerly flow is present over the Dakotas enhanced by an area of High pressure centered in eastern Iowa. The current temperature in Philip, SD is 90F at 3pm.

Saturday:

Warm conditions look to continue as south to southeasterly flow will be ongoing through tomorrow while a lee-cyclogenesis low pressure system takes shape in Colorado. Thunderstorms look likely to the south of South Dakota, but not as much in this area as the low pressure system will move southeastward away from the area. Still, with dewpoints in the upper 50s to low 60s, and temperatures approaching 90F (850 mb temps at 22C, supportive of 88F in Philip per the NAM), convection looks to be possible across the region, especially in the Black Hills and higher elevations in Wyoming. I do not expect a wide spread thunderstorm event, as the trough in the NW will not be pulling into the region until Sunday. I expect some afternoon clouds as storms develop in the Black Hills, holding back high temperatures. I expect a high near 88F, a little less than the NWS is predicting at this time (91F) and a low Saturday night near 65F (NWS: 64F).

Sunday into Monday:

This looks to be the best time period for thunderstorms in this region as a vorticity maximum/500 mb low swings on to the NW coast into the Calgary area. Small vorticity maximums will push over the Dakotas bringing with them enhanced regions of lift to increase the thunderstorm potential. I expect to see a more widespread thunderstorm day in Wyoming into western South Dakota. However, storms may weaken as they approach the Philip area in the evening and over night hours on Sunday. However, a weak nocturnal low level jet may set up over western South Dakota, allowing for thunderstorm propegation to continue into central South Dakota. A low pressure system will develop in southeastern Montana during the evening on Sunday into Monday, sliding a frontal boundary through the area during the day on Monday. This boundary will enhance storm development and a decent thunderstorm threat should be present in western to central South Dakota.

Highs should be a bit cooler if you go by the NAM with 850 mb temps dropping to 19C on Sunday (supportive of 81F), and has trended down from 22C from the 12Z run. MOS on the other hand, says highs should be 94F (GFS) or 89F (ETA). GFS 850 mb temps are a bit higher (24C) supportive of 94F! It is possible the NAM is over doing the cooler temperatures on Sunday. Thus, my high will be a bit closer to MOS: 88F (NWS: 92F) The low should be in the mid to lower 60s, 64F (NWS: 64F).

As for Monday, temperature forecasts become more difficult because MOS is less reliable past two days. GFS MOS ensembles generally predict highs to drop from the lower to mid-90s on Sunday to mid to upper-80s on Monday. 850 mb temps per the NAM on Monday are 24C, supportive of 90F, while the GFS 850 mb temps are 23C, supportive of 88F. I think it is a safe bet to say upper-80s, or 87F (NWS: 88F). Any thunderstorm development could bring down these highs.