National Weather Service Indianapolis IN 300 PM EDT Fri Oct 7 2022 .Short Term...(This evening through Saturday night) Issued at 257 PM EDT Fri Oct 7 2022 ...FROST ADVISORY TONIGHT... * Frost Likely and isolated Freezing conditions Tonight * Sunny and pleasant Saturday Surface analysis early this afternoon shows strong and cold high pressure over the Dakotas, building south. This large high was extending its influence well east across the Great lakes and into the Ohio Valley. Cool north winds were in place across Indiana. GOES16 shows lake clouds steaming off of Lake Michigan, but most of these clouds were failing to reach Central Indiana. Aloft, water vapor imagery showed a broad trough across the eastern 2/3rds of the United States...with some high clouds passing across Illinois and Indiana within the flow. Dew points across much of Central Indiana have fallen to the middle 30s, with lower 30s found upstream. Tonight... Models show prominent NW flow in place aloft overnight with negligible forcing dynamics in place. Surface high pressure over the northern plains states is expected to sag southeast and a ridge axis is shown to extend east across Central Indiana. Time heights and forecast soundings overnight continue to indicate a dry column with subsidence. As heating is lost this evening and as the ridge axis builds, winds will subside leading to ideal radiational cooling conditions with clear skies and light to calm winds. Surface dew points across the area are still above 32 for the most part but additional cold air advection is expected overnight. Currently the 25 percentile NBM temps suggest lows near 32, meaning there are many more scenarios where lows do not fall below 32. Given our current dew points, frost appears to be a slam dunk, but freezing temps will more likely be the exception rather than the rule. Thus will trend overnight lows to mainly the middle 30s, probably with a frost advisory in play rather than a Freeze warning. Saturday and Saturday night... Northwest flow is expected to persist aloft on Saturday and Saturday night, again with negligible forcing dynamics in place. Forecast soundings and Time heights again show a dry column with unreachable convective temperatures on Saturday with a mid level inversion in place aloft. Meanwhile at the surface, the strong high pressure system is expected to sink southward and become more elongated stretching from Kansas toward eastern TN. This will set up a westerly flow across Indiana and also prevent any lake cloud from arriving in our forecast area. Thus we will expect a mostly sunny Saturday and a mostly clear Saturday night under influence of the surface high. Models suggest the beginning of warm air advection on Saturday and Saturday night as the core of cold air with this past system drifts east of Indiana. 850mb temps are shown to rise from below 0C to near 2C by 12Z Sunday. Thus will still stick close to highs in upper 50s and mid to upper 30s on Saturday Night. Again, frost looks to be in play on Saturday Night. && .Long Term...(Sunday through Friday) Issued at 257 PM EDT Fri Oct 7 2022 * Dry conditions and warming trend through mid next week * Next chance for precipitation arrives Wednesday * Cool and dry late week Sunday through Monday Warmer weather returns Sunday as surface high pressure moves east and southwest flow returns. Aloft, guidance suggests troughing remains through Monday few upper level impulses tracking across northern IN Sunday through Monday morning. Precipitation is not expected with these features as moisture return lags due to dry air across much of the region. However, mid-high level clouds will increase late Sunday which could limit overnight lows. Breezy conditions are expected during the day with forecast soundings showing a well-mixed boundary layer with the potential for 20-25mph wind gusts. Monday through Late Next Week... Mid-high clouds should clear out Monday as the aforementioned upper level feature departs. Upper ridging will then build in and help to continue the warming trend as heights increase aloft. In addition, an approaching cold front midweek will lead to increasing southwest flow. Both GFS and EC ensembles show above average 850mb temperature anomalies first half of the week, supporting highs in the mid to upper 70s. Quiet weather is expected through Tuesday with synoptic subsidence from ridging aloft and a dominant surface high across the Mid-atlantic. Rain chances increase Wednesday through early Thursday as the previously mentioned cold front moves through. Not the greatest confidence in widespread significant precipitation yet given the continued dry pattern and surface ridging possibly limiting moisture advection. Although, recent ensemble guidance shows a slightly stronger 850mb jet with deeper moisture across the area. With the jet stream diving so far to the south, there may be enough lift and upper level support along the front for light precipitation to develop, but this will be something to watch over the coming days. Keeping chance wording for PoP during this timeframe with the best chance for rain Wednesday night through Thursday morning. Cooler and drier air will filter in behind the front late week. The coldest air is not expected to arrive until Friday as the trough axis moves east.
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