Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260626_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)
=== ===== === ==== ==== === === === ====
Fri 06/26 18Z 0.77 2310  95  53  10 0.00
Fri 06/26 19Z 0.98 2310  91  56  11 0.06
Fri 06/26 20Z 0.84 2510  87  61  11 0.23
Fri 06/26 21Z 0.96 2711  85  64  12 0.11
Fri 06/26 22Z 0.65 2911  86  63  12 0.15
Fri 06/26 23Z 0.30 3111  87  69  11 0.08
Sat 06/27 00Z 0.30 3112  88  63  11 0.03
Sat 06/27 01Z 0.24 3112  86  42  11 0.00
Sat 06/27 02Z 0.19 3110  82  36  11 0.00
Sat 06/27 03Z 0.17 3109  81  37  11 0.00
Sat 06/27 04Z 0.16 3108  82  39  11 0.00
Sat 06/27 05Z 0.19 3008  83  41  11 0.00
Sat 06/27 06Z 0.19 3009  81  38  11 0.00
Sat 06/27 07Z 0.19 3010  80  36  11 0.00
Sat 06/27 08Z 0.19 3010  80  40  11 0.00
Sat 06/27 09Z 0.19 3110  81  47  11 0.00
Sat 06/27 10Z 0.17 3111  80  56  11 0.00
Sat 06/27 11Z 0.10 3209  77  56  11 0.00
Sat 06/27 12Z 0.08 3207  77  52  11 0.00
Sat 06/27 13Z 0.07 3206  78  53  11 0.00
Sat 06/27 14Z 0.08 3205  80  53  11 0.00
Sat 06/27 15Z 0.09 3105  82  48  11 0.00
Sat 06/27 16Z 0.07 3204  84  44  11 0.00
Sat 06/27 17Z 0.11 3202  85  43  11 0.00
Sat 06/27 18Z 0.11 3202  85  48  11 0.01
Sat 06/27 19Z 0.15 3102  84  46  11 0.01
Sat 06/27 20Z 0.09 3202  84  48  12 0.00
Sat 06/27 21Z 0.07 3302  85  51  12 0.00
Sat 06/27 22Z 0.06 3202  84  52  12 0.00
Sat 06/27 23Z 0.05 3201  84  47  12 0.00
Sun 06/28 00Z 0.03 3301  83  48  12 0.00
Sun 06/28 01Z 0.03 3401  80  53  12 0.00
Sun 06/28 02Z 0.03 0200  79  54  12 0.00
Sun 06/28 03Z 0.03 3400  79  50  12 0.00
Sun 06/28 04Z 0.03 3200  80  46  12 0.00
Sun 06/28 05Z 0.04 3101  82  48  11 0.00
Sun 06/28 06Z 0.03 3202  80  51  11 0.00
Sun 06/28 07Z 0.04 3303  77  50  12 0.00
Sun 06/28 08Z 0.03 3304  76  45  12 0.00
Sun 06/28 09Z 0.03 3406  76  41  11 0.00
Sun 06/28 10Z 0.03 3406  74  37  11 0.00
Sun 06/28 11Z 0.02 3507  72  32  11 0.00
Sun 06/28 12Z 0.02 3507  71  34  11 0.00
Sun 06/28 13Z 0.02 3506  71  33  12 0.00
Sun 06/28 14Z 0.02 3406  73  33  11 0.00
Sun 06/28 15Z 0.02 3505  76  32  11 0.00
Sun 06/28 16Z 0.03 3505  80  29  11 0.00
Sun 06/28 17Z 0.05 3505  82  26  12 0.00
Sun 06/28 18Z 0.07 3504  82  24  12 0.01
Sun 06/28 19Z 0.13 3503  82  23  12 0.01
Sun 06/28 20Z 0.08 3404  82  25  12 0.01
Sun 06/28 21Z 0.08 3303  81  23  12 0.01
Sun 06/28 22Z 0.08 3304  78  19  12 0.01
Sun 06/28 23Z 0.06 3305  74  16  13 0.00
Mon 06/29 00Z 0.03 3407  68   8  13 0.00
Mon 06/29 01Z 0.04 3509  63   8  13 0.00
Mon 06/29 02Z 0.12 0009  61  10  12 0.00
Mon 06/29 03Z 0.14 0109  60  15  12 0.00
Mon 06/29 04Z 0.14 0108  60  18  12 0.00
Mon 06/29 05Z 0.13 0108  59  21  12 0.00

Run total areal avg QPF for the Central_Greens is: 0.73 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