NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260214_0000
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)
=== ===== === ==== ==== === === === ====
Sat 02/14 00Z 0.45 2615  72  35 -10 0.00
Sat 02/14 01Z 0.57 2618  72  36 -10 0.00
Sat 02/14 02Z 0.60 2620  74  47 -10 0.00
Sat 02/14 03Z 0.58 2621  74  56 -10 0.00
Sat 02/14 04Z 0.48 2719  67  45 -10 0.00
Sat 02/14 05Z 0.42 2718  67  46 -10 0.00
Sat 02/14 06Z 0.43 2819  74  63 -10 0.00
Sat 02/14 07Z 0.47 2819  80  75 -11 0.00
Sat 02/14 08Z 0.45 2818  87  75 -11 0.00
Sat 02/14 09Z 0.41 2816  89  72 -10 0.00
Sat 02/14 10Z 0.45 2816  93  76 -11 0.00
Sat 02/14 11Z 0.46 2816  93  79 -11 0.00
Sat 02/14 12Z 0.46 2816  93  80 -10 0.00
Sat 02/14 13Z 0.46 2816  93  79 -10 0.00
Sat 02/14 14Z 0.51 2817  94  70 -10 0.00
Sat 02/14 15Z 0.53 2817  96  54 -10 0.01
Sat 02/14 16Z 0.56 2817  96  38 -10 0.01
Sat 02/14 17Z 0.59 2917  95  29 -10 0.00
Sat 02/14 18Z 0.66 2916  95  23 -10 0.00
Sat 02/14 19Z 0.71 2816  95  19 -10 0.00
Sat 02/14 20Z 0.79 2816  96  18 -10 0.00
Sat 02/14 21Z 0.85 2718  95  19 -10 0.00
Sat 02/14 22Z 0.88 2820  92  20 -10 0.01
Sat 02/14 23Z 0.82 2821  88  21 -10 0.01
Sun 02/15 00Z 0.79 2923  84  22 -10 0.01
Sun 02/15 01Z 0.72 2924  80  21 -10 0.01
Sun 02/15 02Z 0.69 3025  77  20 -10 0.01
Sun 02/15 03Z 0.75 3026  77  18 -11 0.01
Sun 02/15 04Z 0.67 3126  78  17 -11 0.00
Sun 02/15 05Z 0.51 3125  78  17 -12 0.00
Sun 02/15 06Z 0.41 3224  74  16 -11 0.00
Sun 02/15 07Z 0.31 3224  63  16 -11 0.00
Sun 02/15 08Z 0.25 3223  53  16 -11 0.00
Sun 02/15 09Z 0.19 3322  41  17 -10 0.00
Sun 02/15 10Z 0.12 3422  31  20  -9 0.00
Sun 02/15 11Z 0.09 3420  25  21  -9 0.00
Sun 02/15 12Z 0.06 3517  23  22  -9 0.00
Sun 02/15 13Z 0.04 3514  21  21  -9 0.00
Sun 02/15 14Z 0.03 0010  21  23  -8 0.00
Sun 02/15 15Z 0.02 0006  22  25  -8 0.00
Sun 02/15 16Z 0.02 0104  23  30  -8 0.00
Sun 02/15 17Z 0.04 0402  24  40  -7 0.00
Sun 02/15 18Z 0.04 0801  25  42  -7 0.00
Sun 02/15 19Z 0.03 1402  26  41  -6 0.00
Sun 02/15 20Z 0.03 1503  26  34  -6 0.00
Sun 02/15 21Z 0.02 1705  26  35  -6 0.00
Sun 02/15 22Z 0.02 1807  25  45  -6 0.00
Sun 02/15 23Z 0.03 1809  25  53  -6 0.00
Mon 02/16 00Z 0.03 1810  25  54  -5 0.00
Mon 02/16 01Z 0.06 1911  27  54  -6 0.00
Mon 02/16 02Z 0.07 1911  32  63  -6 0.00
Mon 02/16 03Z 0.07 1911  39  70  -6 0.00
Mon 02/16 04Z 0.08 1912  46  80  -6 0.00
Mon 02/16 07Z 0.04 1910  72  87  -6 0.00
Mon 02/16 08Z 0.03 1810  79  89  -6 0.00
Mon 02/16 09Z 0.03 1809  83  91  -6 0.00
Mon 02/16 10Z 0.02 1809  85  92  -5 0.00
Mon 02/16 11Z 0.02 1809  86  92  -5 0.00

Run total areal avg QPF for the greens is: 0.08 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