NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20261001_1200
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)
=== ===== === ==== ==== === === === ====
Thu 10/01 12Z 0.53 2415  92  62  10 0.00
Thu 10/01 13Z 0.64 2418  88  72  10 0.00
Thu 10/01 14Z 0.64 2320  90  84  11 0.00
Thu 10/01 15Z 0.66 2321  91  90  10 0.01
Thu 10/01 16Z 0.86 2320  86  93  10 0.00
Thu 10/01 17Z 0.80 2319  93  87  10 0.00
Thu 10/01 18Z 0.65 2317  86  79  11 0.00
Thu 10/01 19Z 0.65 2318  84  91  12 0.00
Thu 10/01 20Z 0.78 2320  91  99  12 0.00
Thu 10/01 21Z 0.80 2325  95  98  12 0.03
Thu 10/01 22Z 0.83 2330  96  94  13 0.04
Thu 10/01 23Z 0.84 2430  95  92  14 0.03
Fri 10/02 00Z 0.95 2333  94  92  14 0.02
Fri 10/02 01Z 0.96 2433  92  88  14 0.02
Fri 10/02 02Z 0.89 2433  89  69  15 0.01
Fri 10/02 03Z 0.87 2434  87  57  15 0.00
Fri 10/02 04Z 0.90 2436  86  47  16 0.00
Fri 10/02 05Z 1.01 2538  88  52  15 0.01
Fri 10/02 06Z 0.94 2436  88  54  15 0.01
Fri 10/02 07Z 0.95 2438  85  64  16 0.00
Fri 10/02 08Z 0.97 2438  83  62  16 0.00
Fri 10/02 09Z 1.04 2538  87  54  15 0.01
Fri 10/02 10Z 1.06 2537  91  53  15 0.00
Fri 10/02 11Z 1.02 2535  93  62  15 0.01
Fri 10/02 12Z 1.02 2535  94  73  14 0.01
Fri 10/02 13Z 1.02 2533  97  95  14 0.07
Fri 10/02 14Z 1.01 2433  97  98  14 0.23
Fri 10/02 15Z 0.97 2530  98  95  13 0.15
Fri 10/02 16Z 0.75 2723  98  91  13 0.09
Fri 10/02 17Z 0.66 2821  98  92  12 0.05
Fri 10/02 18Z 0.55 2920  97  86  12 0.04
Fri 10/02 19Z 0.48 2919  97  80  11 0.02
Fri 10/02 20Z 0.40 2919  96  76  11 0.01
Fri 10/02 21Z 0.38 3022  96  60  10 0.01
Fri 10/02 22Z 0.35 3022  84  50   9 0.01
Fri 10/02 23Z 0.29 3123  69  19   9 0.00
Sat 10/03 00Z 0.21 3223  53   4   8 0.00
Sat 10/03 01Z 0.17 3324  46   2   7 0.00
Sat 10/03 02Z 0.11 3323  49   2   6 0.00
Sat 10/03 03Z 0.12 3422  57   1   5 0.00
Sat 10/03 04Z 0.19 3323  69   0   4 0.00
Sat 10/03 05Z 0.18 3323  77   0   4 0.00
Sat 10/03 06Z 0.15 3422  79   0   4 0.00
Sat 10/03 07Z 0.11 3421  79   0   3 0.00
Sat 10/03 08Z 0.12 3420  81   1   3 0.00
Sat 10/03 09Z 0.15 3319  81   3   2 0.00
Sat 10/03 10Z 0.13 3318  81   3   2 0.00
Sat 10/03 11Z 0.09 3318  78   3   2 0.00
Sat 10/03 12Z 0.04 3417  75   2   3 0.00
Sat 10/03 13Z 0.03 3416  72   2   3 0.00
Sat 10/03 14Z 0.03 3416  67   2   3 0.00
Sat 10/03 15Z 0.05 3414  62   2   3 0.00
Sat 10/03 16Z 0.07 3313  60   2   3 0.00
Sat 10/03 17Z 0.06 3411  58   2   4 0.00
Sat 10/03 18Z 0.05 3410  57   3   4 0.00
Sat 10/03 19Z 0.03 3408  57   4   4 0.00
Sat 10/03 20Z 0.03 3508  56   4   4 0.00
Sat 10/03 21Z 0.03 3507  55   4   4 0.00
Sat 10/03 22Z 0.05 0006  51   5   4 0.00
Sat 10/03 23Z 0.07 0105  45   5   4 0.00

Run total areal avg QPF for the Central_Greens is: 0.89 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