Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260222_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)
=== ===== === ==== ==== === === === ====
Sun 02/22 06Z 0.12 1509  89  36  -8 0.00
Sun 02/22 07Z 0.14 1511  89  40  -8 0.00
Sun 02/22 08Z 0.12 1612  88  44  -8 0.00
Sun 02/22 09Z 0.10 1612  85  52  -8 0.00
Sun 02/22 10Z 0.10 1612  83  57  -8 0.00
Sun 02/22 11Z 0.10 1612  81  67  -8 0.00
Sun 02/22 12Z 0.10 1612  80  76  -8 0.00
Sun 02/22 13Z 0.12 1512  80  80  -8 0.00
Sun 02/22 14Z 0.15 1512  80  84  -8 0.00
Sun 02/22 15Z 0.19 1413  79  87  -8 0.00
Sun 02/22 16Z 0.25 1313  78  88  -8 0.00
Sun 02/22 17Z 0.29 1313  76  91  -8 0.00
Sun 02/22 18Z 0.34 1313  72  93  -8 0.00
Sun 02/22 19Z 0.37 1314  69  90  -8 0.00
Sun 02/22 20Z 0.38 1313  69  89  -8 0.00
Sun 02/22 21Z 0.41 1213  70  86  -8 0.00
Sun 02/22 22Z 0.48 1114  71  87  -8 0.00
Sun 02/22 23Z 0.58 1017  73  87  -8 0.00
Mon 02/23 00Z 0.63 1019  73  86  -8 0.00
Mon 02/23 01Z 0.58 0920  69  80  -7 0.00
Mon 02/23 02Z 0.60 1021  70  73  -8 0.00
Mon 02/23 03Z 0.64 1022  72  74  -8 0.00
Mon 02/23 04Z 0.67 0923  73  62  -8 0.00
Mon 02/23 05Z 0.70 0824  75  65  -8 0.00
Mon 02/23 06Z 0.72 0824  74  73  -8 0.01
Mon 02/23 07Z 0.73 0825  73  82  -8 0.02
Mon 02/23 08Z 0.69 0726  70  82  -8 0.03
Mon 02/23 09Z 0.74 0628  71  85  -9 0.03
Mon 02/23 10Z 0.77 0629  78  85  -9 0.03
Mon 02/23 11Z 0.75 0531  83  85 -10 0.02
Mon 02/23 12Z 0.73 0532  78  85 -10 0.02
Mon 02/23 13Z 0.77 0532  70  85 -10 0.01
Mon 02/23 14Z 0.65 0432  73  84 -10 0.01
Mon 02/23 15Z 0.61 0431  79  85 -10 0.05
Mon 02/23 16Z 0.59 0330  88  85 -11 0.06
Mon 02/23 17Z 0.48 0330  89  85 -11 0.05
Mon 02/23 18Z 0.37 0231  90  86 -11 0.04
Mon 02/23 19Z 0.26 0132  91  86 -11 0.03
Mon 02/23 20Z 0.18 0033  91  86 -11 0.03
Mon 02/23 21Z 0.12 0033  91  86 -10 0.02
Mon 02/23 22Z 0.11 0034  91  86 -11 0.02
Mon 02/23 23Z 0.11 3536  91  86 -11 0.02
Tue 02/24 00Z 0.12 3537  91  87 -12 0.01
Tue 02/24 01Z 0.11 3537  90  86 -13 0.01
Tue 02/24 02Z 0.12 3536  90  85 -13 0.01
Tue 02/24 03Z 0.16 3534  90  85 -13 0.01
Tue 02/24 04Z 0.26 3430  92  82 -14 0.01
Tue 02/24 05Z 0.35 3429  91  78 -13 0.01
Tue 02/24 06Z 0.35 3330  91  78 -14 0.01
Tue 02/24 07Z 0.40 3330  92  75 -14 0.01
Tue 02/24 08Z 0.62 3328  96  82 -15 0.01
Tue 02/24 09Z 0.53 3227  95  84 -15 0.01
Tue 02/24 10Z 0.38 3226  91  70 -15 0.01
Tue 02/24 11Z 0.34 3224  90  67 -15 0.01
Tue 02/24 12Z 0.33 3123  89  75 -15 0.01
Tue 02/24 13Z 0.32 3123  87  61 -15 0.00
Tue 02/24 14Z 0.32 3123  86  41 -15 0.00
Tue 02/24 15Z 0.31 3121  85  37 -15 0.00
Tue 02/24 16Z 0.35 3121  88  46 -15 0.00
Tue 02/24 17Z 0.36 3019  88  57 -15 0.00

Run total areal avg QPF for the greens is: 0.63 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