NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260328_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)
=== ===== === ==== ==== === === === ====
Sat 03/28 18Z 7.36 2711  68  68 -13 0.00
Sat 03/28 19Z 6.97 2614  75  77 -13 0.00
Sat 03/28 20Z 5.92 2717  78  77 -13 0.00
Sat 03/28 21Z 6.07 2718  75  74 -13 0.01
Sat 03/28 22Z 4.71 2718  74  63 -12 0.01
Sat 03/28 23Z 3.75 2719  80  59 -13 0.01
Sun 03/29 00Z 3.07 2724  78  49 -13 0.00
Sun 03/29 01Z 3.30 2725  81  29 -14 0.00
Sun 03/29 02Z 3.33 2826  79  20 -14 0.00
Sun 03/29 03Z 2.25 2827  77  22 -14 0.00
Sun 03/29 04Z 1.65 2928  76  42 -14 0.00
Sun 03/29 05Z 1.29 2927  83  56 -13 0.00
Sun 03/29 06Z 1.15 2924  89  73 -13 0.00
Sun 03/29 08Z 0.73 2820  92  73 -12 0.00
Sun 03/29 11Z 0.81 2722  92  80 -11 0.00
Sun 03/29 12Z 0.80 2624  92  75 -10 0.00
Sun 03/29 13Z 0.83 2624  88  78 -10 0.00
Sun 03/29 14Z 0.90 2523  83  84  -9 0.00
Sun 03/29 15Z 0.99 2621  81  86  -8 0.00
Sun 03/29 16Z 1.34 2422  81  84  -8 0.00
Sun 03/29 17Z 3.06 2423  75  89  -8 0.00
Sun 03/29 18Z 9.23 2323  66  82  -7 0.00
Sun 03/29 19Z 10.11 2323  61  66  -7 0.00
Sun 03/29 20Z 5.35 2423  62  65  -6 0.00
Sun 03/29 21Z 2.51 2424  65  80  -5 0.00
Sun 03/29 22Z 1.77 2426  66  71  -4 0.00
Sun 03/29 23Z 2.15 2527  64  56  -4 0.00
Mon 03/30 00Z 1.97 2528  60  48  -4 0.00
Mon 03/30 01Z 1.80 2528  59  29  -3 0.00
Mon 03/30 02Z 1.56 2529  59  15  -3 0.00
Mon 03/30 03Z 1.50 2529  58   6  -2 0.00
Mon 03/30 04Z 1.34 2529  58   5  -2 0.00
Mon 03/30 05Z 1.15 2527  57  14  -2 0.00
Mon 03/30 06Z 1.00 2525  64  37  -2 0.00
Mon 03/30 07Z 0.88 2425  73  62  -1 0.00
Mon 03/30 08Z 0.78 2425  78  71  -1 0.00
Mon 03/30 09Z 0.67 2424  80  57  -1 0.00
Mon 03/30 10Z 0.65 2424  83  40   0 0.00
Mon 03/30 11Z 0.72 2427  82  34   0 0.00
Mon 03/30 12Z 0.81 2529  82  59   0 0.00
Mon 03/30 13Z 0.88 2529  87  55   0 0.00
Mon 03/30 14Z 0.96 2530  90  54   0 0.00
Mon 03/30 15Z 0.96 2530  86  48   0 0.00
Mon 03/30 16Z 0.96 2530  85  58   0 0.00
Mon 03/30 17Z 0.93 2529  80  57   1 0.00
Mon 03/30 18Z 1.07 2528  83  47   1 0.00
Mon 03/30 19Z 1.25 2527  84  47   1 0.00
Mon 03/30 20Z 1.49 2526  85  57   1 0.00
Mon 03/30 21Z 1.45 2526  86  60   2 0.00
Mon 03/30 22Z 1.73 2527  84  63   2 0.00
Mon 03/30 23Z 1.95 2628  85  67   2 0.00
Tue 03/31 00Z 1.56 2629  87  60   2 0.00
Tue 03/31 01Z 1.21 2728  91  59   2 0.00
Tue 03/31 02Z 1.02 2726  96  65   2 0.00
Tue 03/31 03Z 0.88 2824  94  70   2 0.01
Tue 03/31 04Z 0.82 2822  96  61   2 0.01
Tue 03/31 05Z 0.73 2720  96  64   2 0.01

Run total areal avg QPF for the Central_Greens is: 0.06 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