Subject: NAM12 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM12_20260130_0600
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)
=== ===== === ==== ==== === === === ====
Fri 01/30 06Z 0.72 2927  80  43 -24 0.00
Fri 01/30 09Z 0.56 3031  76  51 -23 0.00
Fri 01/30 12Z 0.43 3030  79  67 -22 0.00
Fri 01/30 15Z 0.32 3125  81  75 -20 0.00
Fri 01/30 18Z 0.31 3021  83  68 -18 0.00
Fri 01/30 21Z 0.35 3022  85  62 -17 0.00
Sat 01/31 00Z 0.30 3123  88  61 -17 0.00
Sat 01/31 03Z 0.22 3221  89  58 -15 0.00
Sat 01/31 06Z 0.20 3118  87  53 -14 0.00
Sat 01/31 09Z 0.22 3118  86  48 -15 0.00
Sat 01/31 12Z 0.21 3117  86  41 -16 0.00
Sat 01/31 15Z 0.17 3113  86  38 -16 0.00
Sat 01/31 18Z 0.16 3111  88  36 -16 0.00
Sat 01/31 21Z 0.16 3110  88  40 -16 0.00
Sun 02/01 00Z 0.09 3416  85  34 -14 0.00
Sun 02/01 03Z 0.03 0015  81  28 -12 0.00
Sun 02/01 06Z 0.09 0213  71  27 -11 0.00
Sun 02/01 09Z 0.11 0216  62  20 -10 0.00
Sun 02/01 12Z 0.14 0221  60  18  -9 0.00
Sun 02/01 15Z 0.19 0322  57  17  -9 0.00
Sun 02/01 18Z 0.16 0223  52  17  -8 0.00
Sun 02/01 21Z 0.08 0129  48  13  -8 0.00
Mon 02/02 00Z 0.11 0132  47  13  -9 0.00
Mon 02/02 03Z 0.12 0128  49  14  -8 0.00
Mon 02/02 06Z 0.06 3528  59  10  -8 0.00
Mon 02/02 09Z 0.09 3426  57  12  -9 0.00
Mon 02/02 12Z 0.15 3428  49  11  -8 0.00
Mon 02/02 15Z 0.15 3326  41  17  -8 0.00
Mon 02/02 18Z 0.18 3322  39  32  -8 0.00

Run total areal avg QPF for the greens is: 0.00 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