KPDT ProbSvr followup

ProvSvr maxed out at 88%, MESH at about 1.5″ 2029z-2039z.

Wondering if best practice is to lengthen duration of warning in cases when using ProbSvr, since there is some extra lead time compared to when one might issue a warning without it. In our case, we issued at a 30 minute warning (fairly typical) when a 45 minute warning may have been more appropriate given how much sooner ProbSvr can flag a severe potential.

Williams & MacGyver

6/1/15: Bismarck, ND. CI East missed small cell formation.

Noticed that CI-East product didn’t capture the initiation of a small cell NE of Bismarck. At 2015Z a small cell formed (fig 1).  The first time CI showed a probability of initiation occurred at the same time (fig 2).  By 2038Z the cell  developed a small 50dbz+ core. Doesn’t seem like CI-East was able to capture this until it happened. Also, was not overly cloud covered.

Fig 1: CI-East – 2015Z 1st indication in CI

Fig 2: 2015Z: 1st reflectivity appearing.

Fig 3: 2038Z: Small 50dbz core starting.

Forecasters: Cattywampus/CoonieCatEye

6/1/15: 2018Z NUCAPS Profile (Bismarck)

Received a NUCAPS sounding in area relatively cloud free area and modified the sounding using the KISN metar of 88/52 degrees. This gave us a modified CAPE of 2343 J/kg (Fig1). Building confidence in convective developing based on current surface obs, and building cumulus field visibile on Super Rapid Scan Vis. (Fig 2).

Fig 1: 19Z NUCAPS Sounding near KISN (Williston, North Dakota)

Fig 2. Super Rapid Scan at about 20:25Z. Building Cu near Montana and N.Dakota.

Forecasters: Cattywampus/CoonieCatEye

Cell assigned 90 percent chance of severe by CIMSS Prob. Severe Model

A a particularly strong cell moving South of McKay, ID was assigned a 90 percent probability of being severe for 3 consecutive radar volume scans beginning at 1927Z.  A report of 50 mph wind gusts and quarter size hail was reported to NWS Pocatello at 1950Z.  Click on image to see the cursor readout.

John Pendergrast

KPDT ProbSvr at 2011z

Issued a SVR at 2011z for SE of KPDT based in part on the ProbSvr product. Reached 67% at  1950z but came back down to 40% at 2000z. Shot back up to 77% at 2010z. Wanted to see how well it performed for our expected risks of 60mph wind and quarter-sized hail. Growth rates show up as N/A; MESH hail is over 1″, MUCAPE ~1600 J/kg.

Very little lightning, so ENI has not picked up any thunderstorm alerts.

Williams & Macgyver

AFD for KPDX

A well defined vort max on water vapor is moving into the KPDT CWA – very wound up. PWAT values of 1″ are showing up from the GOES sounder in the northeast CWA, which is the climatological max for June 1 at KBOI, the nearest sounding site (to the east).

Looking at RAP, CAPE gradient bisects the CWA at 20z. 0-6km shear is weak at 25 kts, suggesting organized convection will be multicell in nature. 0-1km shear is very low, basically negligible. Very large dry layer evident in the lowest 4000-5000 ft on the KBOI sounding. This suggests the main threats would be wind and possibly marginal hail (especially in the higher elevations) if any storms do turn severe. Really curious to see what the NUCAPS sounding looks like, especially in regards to the dry layer. We’ll have a forthcoming post regarding NUCAPS’ performance. We’ll have to see how the areas of clouds affect the data.

Given the strong shortwave, high PWATs, and weak flow, it appears heavy rain may be a threat from any convection that develops.

Eastern edge of the CWA is in an SPC MRGL outlook.

Jason Williams & MacGyver

6/1/15: Bismarck CWA Discussion

Overview: Main concern in the near term is focused on timing of convective initiation across eastern Montana that will advect into the western Bismarck CWA. Initial synoptic analysis reveals a broad upper low across the Pacific Northwest with mostly zonal flow across the Dakotas and a weak trough over Canada (Fig 1) dipping into the eastern Dakotas.

Fig 1: 00z Tuesday.

Initiation:  As of this writing, no convective cells of significance have developed. There is a lack of large scale forcing over the next few hours. Will initially focus on surface convergence associated with the surface low coupled with convective heating through the afternoon. CIMSS 900mb PWAT indicates plenty of low level moisture advection with south flow ahead of the surface low.  Surface dew points increasing to near 60 degrees. Inspection of the pseudo GOES-R CI data show about 15-20% as of 1915Z (Fig 2).  Estimating time of arrival into Bismarck’s CWA is estimated at 21Z using TOA tool. This seems in line with HRRR which develops around 22Z.  Also feel with cloud cover increasing across that the CI probabilities may be lower than expected.  CIMSS CAPE analysis (Fig 3) favors what are now cloud free areas and show mid 80s over 50s. If development occurs over eastern Montana and advect into this region we could see rapid development. Better dynamics trail the system making noctural convection appear favorable.

Fig 2: CI and Vis. Probabilities around 15-20%

Fig 3: CIMSS CAPE Metars, Overshooting tops, PWAT, etc.



Monitoring:  Plan on monitoring CI probabilities in conjunction with traditional satellite and radar trends for anticipated development. Once convection forms will turn to experimental lightning, severeProb, etc tools.

Forecasters: Cattywampus/CoonieCatEye

GOES-R Products Aid in Mesoscale Analysis over Pocatello CWA

The GOES-R LAP products show an area of elevated CAPE values up to 1500 J/kg in the south-western portion of the Pocatello CWA. The GOES-R LAP PWAT product also shows the highest values (up to 1 inch) over the same area. Looking at some of the LAP products over the past few hours, the instability has increased and the environment has become increasingly more favorable for storm activity. Most of the convection is currently located further west, so expect storm activity to intensify as it moves east into this more favorable environment. The GOES-14-1-Minute visible satellite imagery shows increasing cumulus development over much of the CWA. There is also an area of thicker cloud cover across the northern and western parts of the CWA which may create a differential heating boundary.

Helen Hunt

CAPE comparison near Pendleton, OR

A cu field developed in portions of the Pendleton, OR CWA shortly after 17z. The CAPE derived from GOES is underperforming compared to the RAP CAPE (up to 1800 J/kg). There is a zone where RAP CAPE is 600-1200 J/kg where the GOES estimate is zero. Just to not out-model ourselves, the GOES-derived CAPE does not match up with the cu field’s location.

A positive is that the GOES-R CI has pegged area of possible convection (in a few spots >50%) that lines up very well with where the cu field has developed. The outline of individual cloud elements that is discernible to the eye is also being picked up by the CI algorithm.

Jason Williams and MacGyver

Participants were reminded that these products use a GFS first guess, so if the GFS is way off for whatever reason, the retrievals will likely be off as well, even if they do provide some degree of bias correction - BL

Convective initiation tool keying on leading CU areas

As of 1900Z the CI tool shows some potential for convective development along the leading edge of CU approaching eastern Idaho.  Surface based heating during the course of the afternoon should aid in potential for storm development.

John Pendergrast