NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260709_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)
=== ===== === ==== ==== === === === ====
Thu 07/09 06Z 0.63 2716  81  12  16 0.00
Thu 07/09 07Z 0.65 2817  79   8  16 0.00
Thu 07/09 08Z 0.61 2816  79  12  16 0.00
Thu 07/09 09Z 0.55 2816  78  22  15 0.00
Thu 07/09 10Z 0.53 2815  79  25  15 0.00
Thu 07/09 11Z 0.44 2912  85  30  15 0.00
Thu 07/09 12Z 0.35 2909  89  40  14 0.00
Thu 07/09 13Z 0.28 2807  89  41  14 0.00
Thu 07/09 14Z 0.26 2507  90  51  15 0.00
Thu 07/09 15Z 0.30 2407  89  46  15 0.00
Thu 07/09 16Z 0.43 2508  86  41  15 0.00
Thu 07/09 17Z 0.80 2407  84  53  15 0.00
Thu 07/09 18Z 1.26 2407  83  60  15 0.00
Thu 07/09 19Z 1.33 2307  82  69  16 0.01
Thu 07/09 20Z 1.35 2309  83  77  16 0.05
Thu 07/09 21Z 1.17 2310  84  77  16 0.02
Thu 07/09 22Z 0.61 2310  89  80  16 0.04
Thu 07/09 23Z 0.56 2613  91  79  16 0.26
Fri 07/10 00Z 0.46 2710  92  80  16 0.06
Fri 07/10 01Z 0.34 2609  91  74  16 0.05
Fri 07/10 02Z 0.30 2507  93  69  16 0.01
Fri 07/10 03Z 0.29 2507  96  76  15 0.03
Fri 07/10 04Z 0.30 2508  97  82  15 0.05
Fri 07/10 05Z 0.34 2610  98  79  15 0.05
Fri 07/10 06Z 0.36 2812  97  76  15 0.07
Fri 07/10 07Z 0.33 3014  96  72  14 0.03
Fri 07/10 08Z 0.25 3214  94  67  14 0.01
Fri 07/10 09Z 0.20 3315  91  66  14 0.01
Fri 07/10 10Z 0.21 3316  88  73  13 0.01
Fri 07/10 11Z 0.16 3316  87  70  13 0.01
Fri 07/10 12Z 0.12 3416  87  65  13 0.01
Fri 07/10 13Z 0.09 3415  85  56  12 0.00
Fri 07/10 14Z 0.07 3514  83  55  12 0.00
Fri 07/10 15Z 0.07 3512  82  60  12 0.00
Fri 07/10 16Z 0.14 3511  82  53  12 0.00
Fri 07/10 17Z 0.42 3411  82  47  12 0.00
Fri 07/10 18Z 0.80 3411  83  38  12 0.00
Fri 07/10 19Z 1.27 3310  79  26  12 0.00
Fri 07/10 20Z 1.17 3309  76  20  12 0.00
Fri 07/10 21Z 1.01 3309  74  21  12 0.00
Fri 07/10 22Z 0.58 3310  77  40  12 0.00
Fri 07/10 23Z 0.25 3310  79  30  12 0.00
Sat 07/11 00Z 0.29 3311  79  33  12 0.00
Sat 07/11 01Z 0.28 3312  81  25  11 0.00
Sat 07/11 02Z 0.25 3312  82  25  11 0.00
Sat 07/11 03Z 0.25 3414  82  27  11 0.00
Sat 07/11 04Z 0.14 3413  81  25  10 0.00
Sat 07/11 05Z 0.12 3512  79  24  10 0.00
Sat 07/11 06Z 0.10 0011  78  27  10 0.00
Sat 07/11 07Z 0.12 0109  78  18  10 0.00
Sat 07/11 08Z 0.12 0108  79  19   9 0.00
Sat 07/11 09Z 0.14 0108  80  22   9 0.00
Sat 07/11 10Z 0.13 0108  80  17   9 0.00
Sat 07/11 11Z 0.11 0107  79  12   9 0.00
Sat 07/11 12Z 0.10 0107  77  14   8 0.00
Sat 07/11 13Z 0.14 0007  77  17   8 0.00
Sat 07/11 14Z 0.23 3506  79  21   8 0.00
Sat 07/11 15Z 0.43 3506  80  25   9 0.00
Sat 07/11 16Z 0.48 3508  80  27   9 0.00
Sat 07/11 17Z 0.76 3409  79  31   9 0.00

Run total areal avg QPF for the greens is: 0.78 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