NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

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