Severe Weather Discussion for June 17 - June 20

This is a severe weather discussion focusing on the time period of June 17 to June 20.

Long range forecasts from the Weather Prediction Center show an upper level low entering the Pacific Northwest, provoking ridging in the northern Plains, which is further amplified by an additional trough in the Great Lakes. This ridge then progresses eastward and strengthens, as the upper level low in the Northwest also shifts east, and the Great Lakes trough recedes into Canada. This opens the door for a substantial ridge to push northeast into the Southeast US, as the forecast for early next week shows. At that point, warm and unstable air will flow north into the Central and East US, which will eventually be utilized by an approaching weak trough seen best in Montana by the Day 7 forecast (bottom middle panel).

Projections of convective available potential energy (CAPE), a crucial ingredient for thunderstorms, put instability values over 5000 j/kg. When one considers that 2000 j/kg of CAPE is sufficient for the development and propagation for potentially severe thunderstorms, concern quickly rises over this forecast of incredibly high instability.

Lower level wind speed projections for Wednesday, the same time period as the above image, show a band of enhanced winds extending from Oklahoma into southern Canada due to influence from a storm system draped across the North Plains. Wind speeds inside this band look to meet and exceed 50 knots, meaning any thunderstorms that may form on Wednesday have great potential to be sustained. If there is little wind shear in an environment, a thunderstorm updraft can become entangled with the downdraft, which then weakens the storm. This phenomenon is what creates 'pulse storms', or those small-celled thunderstorms that form and then die off just as fast. However, with forecasts showing substantial lower level winds for Wednesday, more organized, sustained convection may be anticipated.

Additional updates concerning this situation will be published in the near future.

Andrew

Release Date for Preliminary 2014-2015 Winter Forecast

The Preliminary 2014-2015 Winter Forecast will be released this Saturday, June 14, at 12:00 PM Central Time.

Analogs, an analysis of the factors driving this winter, as well as preliminary estimates of temperature and precipitation patterns will be discussed.

Andrew

What Are The Models Saying This Winter? - GFDL_FLORb01 Model

In the next part of this series, we're going to analyze yet another version of the GFDL model, named the GFDL_FLORb01 model. It's quite a mouthful, so we'll just refer to it as another version of its parent GFDL model.

This version of the GFDL model shows a pretty cold start to winter. As the image above shows, the December 2014 forecast calls for widespread below normal temperatures, concentrated in the Plains, and spilling east across most of the land east of the Front Range. This cold also extends into southeastern Canada, but from there, warmth dominates to the north. We see intense warm temperature anomalies concentrated near the Arctic Circle, which may indicate the negative phase of the Arctic Oscillation. The negative phase of the Arctic Oscillation (AO) can be defined by warm weather over the Arctic Circle, which can lead to a weakening of the polar vortex. The polar vortex then releases vast quantities of cold air to lower latitudes, which can include North America. We have yet to see if this is the case, but if this forecast were to verify, we would see potentially a repeat of last winter's cold.

The precipitation forecast from the GFDL_FLORb01 model shows anomalously dry weather spread out across the Pacific Northwest and into British Columbia, with wetter than normal conditions located in the Southwest, especially in California, and into Arizona. This wetter than normal trend continues across the Southern Plains, into the Ohio Valley, and on to the Mid-Atlantic. From there, we see spots of dry conditions extending from the Midwest into the Great Lakes, as well as some dryness in the Southeast. This goes strongly against the expected El Nino's typical winter precipitation pattern, and for that reason, I am a bit skeptical.

This is likely an experimental model not intended for operational use, so confidence is already low. However, the somewhat-odd precipitation pattern lowers my confidence further.

Additional models will be analyzed in coming days.

Andrew

Mid-June Severe Weather Outbreak Still Looking Possible

The mid-June severe weather outbreak we first discussed in the middle of May still looks to pose a threat to the United States.

500mb forecast heights from forecast Day 3 (top right) across and down to Day 7 (bottom middle).

Long range guidance from the Weather Prediction Center shows troughing developing in the Pacific Northwest beginning on forecast Day 4 (top-middle panel), and continuing through Day 7 (bottom middle panel). This troughing along the West Coast then forces a dome of high pressure to rise up in the Central and East US, a feature that was predicted in the linked post above with the help of the Bering Sea Rule. It is this dome of high pressure that I believe may very well allow for this/these severe weather episode(s).

Instability forecast for June 16th

The GFS model has been showing vast expanses of very high amounts of instability overspreading portions of the Central US for multiple forecast runs now, with the most recent forecast shown above. The gist of this scenario is that a large plume of instability would be pulled north into the southern and central Plains, likely kicking off what might be a multi-day severe weather event. From there, guidance tends to shift that body of instability east, like the image above shows. However, with location of this instability plume and timing concerns raising uncertainty, we will need more time to see just how extensive this potential event may be.

Andrew

What Are The Models Saying This Winter? - GFDL_FLORa06 Model

Today, we will be taking a look at the GFDL_FLORa06 model, which we'll shorten to call another version of the GFDL model.

This version of the GFDL model has a rather neutral start to winter in the temperature department. We see that this forecast has an abundance of warmer than normal temperatures in Canada, partially extnding down into the upper Midwest and New England areas. This sort of temperature pattern resembles the El Nino pattern, where one typically sees above normal temperatures in the North and cooler weather in the South. However, that is where the similarities end. This version of the GFDL model then produces cooler than normal weather across the Rockies, pushing south into Texas as well. Normal temperatures are then projected across the remainder of the nation, going against typical El Nino winter temperature patterns.

The precipitation forecast from this particular version of the GFDL model is also somewhat different from a typical El Nino winter. In normal El Nino winters, we tend to see wet weather in the Southwest, dry in the Northwest, and continued drought-esque precipitation patterns in the Ohio Valley. Wetter than normal conditions are then observed across the East Coast. In this model projection, we do see a dry Pacific Northwest and wet Southwest to kick off winter, but then an area of above normal precipitation is observed across the Plains and Midwest. The tell-tale dry signal is then forecasted in the south central Plains into the Ohio Valley, but rather than see wet conditions along the East Coast, we see dry conditions. Anomalously above normal precipitation is forecasted in the Southeast, but it does not extend into the East Coast.

Because this appears to be an experimental derivation forecast from the parent GFDL model, confidence in this forecast is low.

Additional models will be analyzed in coming days.

Andrew