NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260202_1800
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)
=== ===== === ==== ==== === === === ====
Mon 02/02 18Z 0.16 3317  68  15 -10 0.00
Mon 02/02 19Z 0.20 3319  66  12  -9 0.00
Mon 02/02 20Z 0.22 3321  67  10 -10 0.00
Mon 02/02 21Z 0.24 3322  69   7 -10 0.00
Tue 02/03 00Z 0.18 3319  56  10  -9 0.00
Tue 02/03 01Z 0.14 3317  51  20  -9 0.00
Tue 02/03 02Z 0.09 3415  48  36  -9 0.00
Tue 02/03 04Z 0.10 3311  52  59  -9 0.00
Tue 02/03 05Z 0.13 3211  56  62  -9 0.00
Tue 02/03 06Z 0.15 3211  56  64 -10 0.00
Tue 02/03 07Z 0.16 3111  57  62 -10 0.00
Tue 02/03 08Z 0.18 3111  58  61 -10 0.00
Tue 02/03 09Z 0.18 3111  58  59  -9 0.00
Tue 02/03 10Z 0.15 3109  56  57  -9 0.00
Tue 02/03 11Z 0.13 3108  55  57  -9 0.00
Tue 02/03 12Z 0.12 3107  55  54  -9 0.00
Tue 02/03 13Z 0.12 3006  56  40  -9 0.00
Tue 02/03 14Z 0.13 2906  57  30  -9 0.00
Tue 02/03 15Z 0.12 2705  59  24 -10 0.00
Tue 02/03 16Z 0.13 2605  60  21 -10 0.00
Tue 02/03 17Z 0.13 2505  60  45 -10 0.00
Tue 02/03 18Z 0.15 2405  59  66 -10 0.00
Tue 02/03 19Z 0.19 2305  58  77 -11 0.00
Tue 02/03 20Z 0.23 2306  59  84 -11 0.00
Tue 02/03 21Z 0.24 2306  63  82 -11 0.00
Tue 02/03 22Z 0.25 2307  70  68 -12 0.00
Tue 02/03 23Z 0.26 2408  80  57 -12 0.00
Wed 02/04 00Z 0.30 2409  87  56 -12 0.00
Wed 02/04 01Z 0.34 2509  90  60 -12 0.00
Wed 02/04 02Z 0.31 2509  91  66 -12 0.00
Wed 02/04 03Z 0.30 2509  91  68 -13 0.00
Wed 02/04 04Z 0.37 2610  91  72 -13 0.00
Wed 02/04 05Z 0.44 2712  92  78 -13 0.00
Wed 02/04 06Z 0.49 2712  92  80 -14 0.00
Wed 02/04 07Z 0.51 2712  92  79 -14 0.00
Wed 02/04 08Z 0.59 2814  93  65 -14 0.00
Wed 02/04 09Z 0.64 2815  93  63 -15 0.01
Wed 02/04 10Z 0.57 2915  92  66 -15 0.01
Wed 02/04 12Z 0.36 2913  88  68 -15 0.01
Wed 02/04 13Z 0.25 3113  86  63 -15 0.01
Wed 02/04 14Z 0.20 3213  86  56 -15 0.01
Wed 02/04 15Z 0.23 3215  88  53 -14 0.00
Wed 02/04 16Z 0.27 3216  90  46 -14 0.00
Wed 02/04 17Z 0.33 3217  90  43 -14 0.00
Wed 02/04 18Z 0.40 3117  86  41 -14 0.00
Wed 02/04 19Z 0.48 3117  84  41 -14 0.00
Wed 02/04 20Z 0.55 3017  83  40 -14 0.00
Wed 02/04 21Z 0.57 3017  84  38 -14 0.00
Wed 02/04 22Z 0.56 3018  84  36 -14 0.00
Wed 02/04 23Z 0.53 3018  85  34 -14 0.00
Thu 02/05 00Z 0.44 3018  86  33 -13 0.00
Thu 02/05 01Z 0.35 3116  85  32 -13 0.00
Thu 02/05 02Z 0.27 3115  84  31 -13 0.00
Thu 02/05 03Z 0.24 3114  83  32 -12 0.00
Thu 02/05 04Z 0.23 3113  83  32 -13 0.00
Thu 02/05 05Z 0.23 3012  84  33 -13 0.00

Run total areal avg QPF for the greens is: 0.05 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