NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20251008_1800
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)
=== ===== === ==== ==== === === === ====
Wed 10/08 18Z 0.14 3417  86  40   3 0.00
Wed 10/08 19Z 0.50 3518  81  18   3 0.00
Wed 10/08 20Z 0.47 3515  76  37   2 0.00
Wed 10/08 21Z 0.42 3414  77  47   2 0.00
Wed 10/08 22Z 0.30 3319  83  59   2 0.01
Wed 10/08 23Z 0.14 3422  85  63   1 0.00
Thu 10/09 00Z 0.10 3521  87  43   1 0.00
Thu 10/09 01Z 0.12 3521  90  25   0 0.00
Thu 10/09 02Z 0.17 3521  91  10   0 0.00
Thu 10/09 03Z 0.08 3521  90   2  -1 0.00
Thu 10/09 04Z 0.04 3521  83   2  -2 0.00
Thu 10/09 05Z 0.05 3421  82   6  -2 0.00
Thu 10/09 06Z 0.06 3422  82  11  -3 0.00
Thu 10/09 07Z 0.08 3423  78   8  -3 0.00
Thu 10/09 08Z 0.07 3425  75   5  -4 0.00
Thu 10/09 09Z 0.05 3425  76   5  -4 0.00
Thu 10/09 10Z 0.06 3425  79   6  -5 0.00
Thu 10/09 11Z 0.10 3424  79   7  -5 0.00
Thu 10/09 12Z 0.10 3423  78   7  -5 0.00
Thu 10/09 13Z 0.07 3421  77   7  -5 0.00
Thu 10/09 14Z 0.06 3419  76   7  -5 0.00
Thu 10/09 15Z 0.10 3417  75   6  -5 0.00
Thu 10/09 16Z 0.13 3416  71   5  -4 0.00
Thu 10/09 17Z 0.12 3415  66   4  -4 0.00
Thu 10/09 18Z 0.11 3415  62   3  -3 0.00
Thu 10/09 19Z 0.09 3414  58   3  -3 0.00
Thu 10/09 20Z 0.04 3514  53   4  -2 0.00
Thu 10/09 21Z 0.02 3414  47   4  -2 0.00
Thu 10/09 22Z 0.03 3514  39   4  -1 0.00
Thu 10/09 23Z 0.03 3515  33   4   0 0.00
Fri 10/10 00Z 0.03 3514  30   6   0 0.00
Fri 10/10 01Z 0.04 3513  28   7   0 0.00
Fri 10/10 02Z 0.05 0010  27   7   0 0.00
Fri 10/10 03Z 0.04 0007  26   7   0 0.00
Fri 10/10 04Z 0.03 3505  24   8   1 0.00
Fri 10/10 05Z 0.02 3404  23   9   1 0.00
Fri 10/10 06Z 0.03 3303  22   9   1 0.00
Fri 10/10 07Z 0.06 2903  21   8   2 0.00
Fri 10/10 08Z 0.10 2704  20   8   2 0.00
Fri 10/10 09Z 0.13 2605  19   8   2 0.00
Fri 10/10 10Z 0.14 2606  18   8   2 0.00
Fri 10/10 11Z 0.16 2507  19   8   3 0.00
Fri 10/10 12Z 0.17 2508  21   7   3 0.00
Fri 10/10 13Z 0.18 2508  22   7   3 0.00
Fri 10/10 14Z 0.17 2408  22   7   3 0.00
Fri 10/10 15Z 0.18 2309  23   7   4 0.00
Fri 10/10 16Z 0.19 2209  23   6   4 0.00
Fri 10/10 17Z 0.22 2210  22   5   4 0.00
Fri 10/10 18Z 0.24 2211  21   5   4 0.00
Fri 10/10 19Z 0.28 2113  20   5   4 0.00
Fri 10/10 20Z 0.31 2114  18   5   5 0.00
Fri 10/10 21Z 0.32 2115  16   5   5 0.00
Fri 10/10 22Z 0.35 2218  15   6   6 0.00
Fri 10/10 23Z 0.39 2220  15   6   6 0.00
Sat 10/11 00Z 0.42 2321  18   6   6 0.00
Sat 10/11 01Z 0.42 2322  21   6   7 0.00
Sat 10/11 02Z 0.45 2323  25   5   7 0.00
Sat 10/11 03Z 0.47 2424  30   5   7 0.00
Sat 10/11 04Z 0.44 2423  30   6   7 0.00
Sat 10/11 05Z 0.43 2422  35   6   7 0.00

Run total areal avg QPF for the Central_Greens is: 0.01 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