NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20251009_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)
=== ===== === ==== ==== === === === ====
Thu 10/09 06Z 0.23 0028  82   6  -3 0.00
Thu 10/09 07Z 0.14 0027  77   7  -4 0.00
Thu 10/09 08Z 0.13 3525  78   7  -4 0.00
Thu 10/09 09Z 0.16 3524  78   6  -5 0.00
Thu 10/09 10Z 0.26 3424  80   6  -5 0.00
Thu 10/09 11Z 0.30 3424  82   7  -6 0.00
Thu 10/09 12Z 0.32 3424  81   7  -6 0.00
Thu 10/09 13Z 0.31 3422  79   8  -6 0.00
Thu 10/09 14Z 0.42 3320  77   7  -5 0.00
Thu 10/09 15Z 0.49 3318  76   5  -5 0.00
Thu 10/09 16Z 0.45 3315  74   5  -5 0.00
Thu 10/09 17Z 0.48 3314  71   5  -4 0.00
Thu 10/09 18Z 0.49 3313  67   4  -4 0.00
Thu 10/09 19Z 0.45 3313  63   3  -3 0.00
Thu 10/09 20Z 0.33 3414  59   3  -3 0.00
Thu 10/09 21Z 0.22 3414  55   4  -2 0.00
Thu 10/09 22Z 0.18 3414  49   5  -2 0.00
Thu 10/09 23Z 0.15 3414  45   5  -2 0.00
Fri 10/10 00Z 0.12 3413  43   5  -1 0.00
Fri 10/10 01Z 0.12 3412  40   6  -1 0.00
Fri 10/10 02Z 0.12 3312  39   6   0 0.00
Fri 10/10 03Z 0.11 3311  39   7   0 0.00
Fri 10/10 04Z 0.09 3309  36   7   0 0.00
Fri 10/10 05Z 0.08 3307  33   7   0 0.00
Fri 10/10 06Z 0.09 3206  30   7   1 0.00
Fri 10/10 07Z 0.10 3005  27   7   1 0.00
Fri 10/10 08Z 0.12 2905  25   8   1 0.00
Fri 10/10 09Z 0.15 2806  23   8   2 0.00
Fri 10/10 10Z 0.16 2807  22   9   2 0.00
Fri 10/10 11Z 0.18 2708  22   9   2 0.00
Fri 10/10 12Z 0.17 2707  23  12   2 0.00
Fri 10/10 13Z 0.16 2607  24  14   2 0.00
Fri 10/10 14Z 0.16 2507  25  16   2 0.00
Fri 10/10 15Z 0.16 2407  26  14   2 0.00
Fri 10/10 16Z 0.16 2308  27  11   3 0.00
Fri 10/10 17Z 0.16 2208  28  10   3 0.00
Fri 10/10 18Z 0.18 2209  28   8   3 0.00
Fri 10/10 19Z 0.20 2111  26   7   4 0.00
Fri 10/10 20Z 0.22 2112  24   7   4 0.00
Fri 10/10 21Z 0.25 2114  22   7   4 0.00
Fri 10/10 22Z 0.31 2218  20   6   5 0.00
Fri 10/10 23Z 0.36 2221  19   6   5 0.00
Sat 10/11 00Z 0.38 2321  22   5   6 0.00
Sat 10/11 01Z 0.40 2321  24   5   6 0.00
Sat 10/11 02Z 0.41 2421  28   6   6 0.00
Sat 10/11 03Z 0.41 2421  32   9   6 0.00
Sat 10/11 04Z 0.43 2421  35   9   6 0.00
Sat 10/11 05Z 0.42 2421  38   9   6 0.00
Sat 10/11 06Z 0.42 2520  43  10   6 0.00
Sat 10/11 07Z 0.40 2519  47  12   5 0.00
Sat 10/11 08Z 0.37 2517  50  12   5 0.00
Sat 10/11 09Z 0.31 2515  47  10   6 0.00
Sat 10/11 10Z 0.26 2513  45  11   6 0.00
Sat 10/11 11Z 0.20 2610  43  11   6 0.00
Sat 10/11 12Z 0.15 2507  44  11   6 0.00
Sat 10/11 13Z 0.11 2405  43  10   6 0.00
Sat 10/11 14Z 0.09 2305  41  10   6 0.00
Sat 10/11 15Z 0.08 2205  39  11   6 0.00
Sat 10/11 16Z 0.09 2205  39  11   7 0.00
Sat 10/11 17Z 0.10 2205  42  11   7 0.00

Run total areal avg QPF for the greens is: 0.00 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