Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260503_0600
Using the MB925 to MB850 layer.
Assumes greens are orthogonal to 270 degree winds.
925-850 mb Layer Average Wind/RH. Avg QPF over the greens.
Date Time Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Sun 05/03 06Z 0.33 3211 92 49 -4 0.00
Sun 05/03 07Z 0.38 3213 92 51 -5 0.00
Sun 05/03 08Z 0.45 3316 92 51 -5 0.01
Sun 05/03 09Z 0.41 3317 90 51 -5 0.00
Sun 05/03 10Z 0.39 3319 87 49 -5 0.00
Sun 05/03 11Z 0.38 3320 84 49 -5 0.00
Sun 05/03 12Z 0.52 3319 83 52 -5 0.00
Sun 05/03 13Z 1.75 3318 81 56 -5 0.00
Sun 05/03 14Z 3.43 3317 78 53 -5 0.00
Sun 05/03 15Z 5.17 3217 77 48 -4 0.00
Sun 05/03 16Z 6.41 3218 73 43 -4 0.00
Sun 05/03 17Z 8.02 3118 72 40 -4 0.00
Sun 05/03 18Z 9.07 3118 68 39 -3 0.00
Sun 05/03 19Z 9.65 3118 65 37 -3 0.00
Sun 05/03 20Z 9.98 3018 63 37 -3 0.00
Sun 05/03 21Z 10.79 3019 63 40 -2 0.00
Sun 05/03 22Z 11.20 3020 64 37 -2 0.00
Sun 05/03 23Z 7.63 2920 65 33 -2 0.00
Mon 05/04 00Z 2.24 2921 65 26 -2 0.00
Mon 05/04 01Z 2.65 2922 65 12 -2 0.00
Mon 05/04 02Z 1.68 2821 61 3 -2 0.00
Mon 05/04 03Z 1.06 2821 58 11 -1 0.00
Mon 05/04 04Z 0.99 2722 66 57 -1 0.00
Mon 05/04 05Z 0.81 2722 79 87 0 0.01
Mon 05/04 06Z 0.69 2623 85 92 0 0.02
Mon 05/04 07Z 0.74 2627 88 94 0 0.04
Mon 05/04 08Z 0.84 2529 87 90 0 0.04
Mon 05/04 09Z 0.88 2529 90 87 0 0.02
Mon 05/04 10Z 0.92 2531 91 79 0 0.02
Mon 05/04 11Z 0.97 2533 93 91 0 0.03
Mon 05/04 12Z 0.95 2533 94 90 1 0.03
Mon 05/04 13Z 0.92 2630 94 90 1 0.03
Mon 05/04 14Z 0.89 2628 95 80 1 0.03
Mon 05/04 15Z 0.93 2527 95 53 1 0.02
Mon 05/04 16Z 1.10 2524 95 22 1 0.01
Mon 05/04 17Z 1.57 2524 95 17 1 0.01
Mon 05/04 18Z 3.26 2523 92 13 1 0.01
Mon 05/04 19Z 5.45 2522 89 21 2 0.00
Mon 05/04 20Z 3.82 2521 86 35 2 0.00
Mon 05/04 21Z 2.86 2520 85 31 3 0.00
Mon 05/04 22Z 1.68 2420 84 18 3 0.00
Mon 05/04 23Z 0.97 2421 82 14 4 0.00
Tue 05/05 00Z 0.82 2422 80 15 5 0.00
Tue 05/05 01Z 0.76 2323 78 12 5 0.00
Tue 05/05 02Z 0.78 2326 77 11 6 0.00
Tue 05/05 03Z 0.84 2328 80 11 6 0.00
Tue 05/05 04Z 0.89 2330 82 10 6 0.00
Tue 05/05 05Z 0.89 2232 84 9 7 0.00
Tue 05/05 06Z 0.99 2333 86 10 7 0.00
Tue 05/05 07Z 0.95 2332 86 7 6 0.01
Tue 05/05 08Z 0.70 2329 79 6 8 0.00
Tue 05/05 09Z 0.65 2230 84 9 8 0.01
Tue 05/05 10Z 0.68 2231 88 29 8 0.01
Tue 05/05 11Z 0.64 2231 89 78 8 0.01
Tue 05/05 12Z 0.73 2332 91 81 8 0.00
Tue 05/05 13Z 0.82 2331 92 77 8 0.00
Tue 05/05 14Z 0.94 2330 93 86 8 0.01
Tue 05/05 15Z 0.96 2327 91 70 8 0.00
Tue 05/05 16Z 1.63 2325 92 72 8 0.00
Tue 05/05 17Z 0.93 2221 92 45 8 0.01
Run total areal avg QPF for the greens is: 0.39 inches.
Froude Number (Frd#):
Frd# < 0.5 Flow is subcritical and blocked.
Upslope clouds/precip backed farther upwind of and up to mtn crest.
W Upslope snow favors eastern Champlain Valley, BTV, and Western slopes.
Gap winds possible.
Frd# 0.5-1 Flow is subcritical/slow moving/blocked.
Upslope clouds/precip falls immediately upwind of mtn crest.
W Upslope snow favors western slopes to the Green Mt. spine including:
Montgomery,Underhill,Jericho,Bolton,Richmond,Huntington,Lincoln.
Gap winds possible.
Frd# 1-2 Flow is critical.
With strong winds, Mountain waves/downslope winds possible.
Precip falls close to mountain ridge crests and on lee side.
W Upslope snow favors Green Mt Spine,Jay,Stowe,Waterbury,NE Kingdom.
Froude > 2 Flow is supercritical/unblocked(rapid flow).
Air flows freely over terrain.
Persistent upslope snow not favored. Scattered snow showers and flurries.
Relative Humidity (RH):
925-850 mb RH > 90% needed for upslope precipitation.
with 700mb RH > 70% favors upslope snow.
with 700mb RH > 90% greater amounts of W upslope snow possible.
850mb Temperature (T degC) Westerly Upslope Snow Ratios: (Avg=28:1)
T > -11 10-15:1
T -11 to -15 25-35:1
T < -15 15-20:1