Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260118_0600
Using the MB925 to MB850 layer.
Assumes Central_Greens are orthogonal to 260 degree winds.
925-850 mb Layer Average Wind/RH. Avg QPF over the Central_Greens.
Date Time Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Sun 01/18 06Z 0.73 2422 93 56 -7 0.00
Sun 01/18 07Z 0.82 2424 94 45 -7 0.00
Sun 01/18 08Z 0.77 2422 94 32 -7 0.01
Sun 01/18 09Z 0.68 2521 91 39 -8 0.00
Sun 01/18 10Z 0.62 2520 88 64 -8 0.00
Sun 01/18 11Z 0.58 2519 86 73 -8 0.00
Sun 01/18 13Z 0.79 2522 79 83 -9 0.00
Sun 01/18 14Z 0.89 2523 67 84 -10 0.00
Sun 01/18 15Z 0.92 2421 63 85 -10 0.00
Sun 01/18 16Z 1.13 2420 69 89 -11 0.00
Sun 01/18 17Z 1.24 2418 70 89 -11 0.00
Sun 01/18 18Z 2.54 2414 75 92 -11 0.00
Sun 01/18 20Z 0.59 2406 78 85 -11 0.00
Sun 01/18 21Z 0.29 2604 75 74 -11 0.00
Sun 01/18 22Z 0.12 2402 72 72 -11 0.00
Sun 01/18 23Z 0.04 3302 71 47 -10 0.00
Mon 01/19 00Z 0.08 0203 72 47 -10 0.00
Mon 01/19 01Z 0.05 0102 72 85 -10 0.00
Mon 01/19 02Z 0.09 0204 76 89 -10 0.00
Mon 01/19 03Z 0.03 3505 77 90 -10 0.00
Mon 01/19 04Z 0.04 3406 80 87 -11 0.00
Mon 01/19 05Z 0.05 0006 83 90 -11 0.00
Mon 01/19 06Z 0.07 0007 84 91 -12 0.00
Mon 01/19 07Z 0.05 3507 84 83 -12 0.01
Mon 01/19 08Z 0.03 3506 85 79 -12 0.00
Mon 01/19 09Z 0.02 3404 85 63 -12 0.00
Mon 01/19 10Z 0.06 3103 85 56 -12 0.00
Mon 01/19 11Z 0.12 2704 86 48 -12 0.00
Mon 01/19 12Z 0.18 2606 88 37 -12 0.00
Mon 01/19 13Z 0.21 2507 90 21 -13 0.00
Mon 01/19 14Z 0.23 2307 90 20 -13 0.00
Mon 01/19 15Z 0.32 2209 91 63 -13 0.00
Mon 01/19 16Z 0.54 2211 92 85 -13 0.00
Mon 01/19 17Z 1.58 2113 92 81 -13 0.00
Mon 01/19 18Z 3.40 2116 90 81 -13 0.00
Mon 01/19 19Z 4.93 2217 88 83 -13 0.00
Mon 01/19 20Z 4.19 2319 90 83 -13 0.00
Mon 01/19 21Z 3.07 2322 91 83 -13 0.00
Mon 01/19 22Z 3.97 2426 92 73 -14 0.00
Mon 01/19 23Z 1.67 2427 87 63 -14 0.01
Tue 01/20 00Z 1.53 2427 87 61 -14 0.01
Tue 01/20 01Z 1.59 2428 86 59 -14 0.00
Tue 01/20 02Z 2.32 2430 84 51 -14 0.00
Tue 01/20 03Z 4.35 2430 85 56 -15 0.00
Tue 01/20 04Z 4.18 2430 85 55 -16 0.00
Tue 01/20 05Z 4.25 2531 79 45 -17 0.00
Tue 01/20 06Z 1.56 2433 81 61 -16 0.00
Tue 01/20 07Z 1.52 2534 86 36 -17 0.00
Tue 01/20 08Z 1.39 2632 84 37 -17 0.00
Tue 01/20 09Z 1.41 2628 86 31 -17 0.00
Tue 01/20 10Z 1.48 2626 89 21 -18 0.00
Tue 01/20 11Z 1.65 2625 90 21 -18 0.00
Tue 01/20 12Z 1.57 2623 89 26 -19 0.00
Tue 01/20 13Z 1.26 2622 85 28 -19 0.00
Tue 01/20 14Z 1.31 2620 81 34 -19 0.00
Tue 01/20 15Z 1.73 2618 81 44 -20 0.00
Tue 01/20 16Z 3.11 2517 82 70 -20 0.00
Tue 01/20 17Z 8.97 2516 84 75 -20 0.00
Run total areal avg QPF for the Central_Greens is: 0.04 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