Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260626_1200
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 12Z 0.22 2012  97  86  10 0.00
Fri 06/26 13Z 0.23 2111  97  86  10 0.00
Fri 06/26 14Z 0.28 2211  97  91  11 0.01
Fri 06/26 15Z 0.31 2310  98  93  11 0.00
Fri 06/26 16Z 0.28 2308  97  88  11 0.02
Fri 06/26 17Z 0.29 2407  97  74  11 0.01
Fri 06/26 18Z 0.30 2407  94  74  11 0.00
Fri 06/26 19Z 0.37 2307  87  61  12 0.00
Fri 06/26 20Z 0.42 2306  88  61  11 0.03
Fri 06/26 21Z 0.40 2306  86  68  12 0.23
Fri 06/26 22Z 0.36 2707  86  62  12 0.24
Fri 06/26 23Z 0.23 3111  85  64  12 0.21
Sat 06/27 00Z 0.25 3112  83  36  12 0.02
Sat 06/27 01Z 0.18 3211  81  39  12 0.00
Sat 06/27 02Z 0.15 3210  79  41  12 0.00
Sat 06/27 03Z 0.20 3110  81  40  11 0.00
Sat 06/27 04Z 0.17 3109  83  39  11 0.00
Sat 06/27 05Z 0.17 3008  84  40  11 0.00
Sat 06/27 06Z 0.19 3008  84  38  11 0.00
Sat 06/27 07Z 0.21 3009  85  38  11 0.00
Sat 06/27 08Z 0.20 3008  86  38  11 0.00
Sat 06/27 09Z 0.19 3009  87  41  11 0.00
Sat 06/27 10Z 0.15 3108  88  41  11 0.00
Sat 06/27 11Z 0.14 3108  90  40  11 0.00
Sat 06/27 12Z 0.11 3207  91  35  10 0.00
Sat 06/27 13Z 0.11 3106  93  35  10 0.00
Sat 06/27 14Z 0.10 3206  95  36  10 0.00
Sat 06/27 15Z 0.05 3304  94  37  10 0.00
Sat 06/27 16Z 0.08 3002  94  40  10 0.00
Sat 06/27 17Z 0.12 2702  92  38  11 0.01
Sat 06/27 18Z 0.17 2703  90  39  11 0.01
Sat 06/27 19Z 0.25 2803  89  40  11 0.01
Sat 06/27 20Z 0.22 2803  88  36  11 0.01
Sat 06/27 21Z 0.20 3004  87  37  12 0.00
Sat 06/27 22Z 0.12 3104  87  40  12 0.00
Sat 06/27 23Z 0.06 3203  87  45  12 0.00
Sun 06/28 00Z 0.05 3302  86  46  12 0.00
Sun 06/28 01Z 0.03 3402  84  49  12 0.00
Sun 06/28 02Z 0.03 0002  83  47  12 0.00
Sun 06/28 03Z 0.03 0002  83  46  11 0.00
Sun 06/28 04Z 0.05 0103  82  46  11 0.00
Sun 06/28 05Z 0.02 0003  82  48  11 0.00
Sun 06/28 06Z 0.02 3503  81  41  11 0.00
Sun 06/28 07Z 0.02 3503  80  40  11 0.00
Sun 06/28 08Z 0.02 3504  78  27  11 0.00
Sun 06/28 09Z 0.02 3404  77  24  11 0.00
Sun 06/28 10Z 0.03 3405  77  23  11 0.00
Sun 06/28 11Z 0.02 3406  75  22  11 0.00
Sun 06/28 12Z 0.02 3406  73  25  11 0.00
Sun 06/28 13Z 0.02 3506  72  25  11 0.00
Sun 06/28 14Z 0.03 0005  73  27  11 0.00
Sun 06/28 15Z 0.05 0004  76  30  11 0.00
Sun 06/28 16Z 0.06 0104  79  32  11 0.00
Sun 06/28 17Z 0.09 0103  80  30  11 0.00
Sun 06/28 18Z 0.13 0004  79  26  11 0.00
Sun 06/28 19Z 0.14 3504  80  22  12 0.00
Sun 06/28 20Z 0.15 3504  81  22  12 0.00
Sun 06/28 21Z 0.10 3404  81  24  12 0.01
Sun 06/28 22Z 0.06 3405  80  27  12 0.01
Sun 06/28 23Z 0.06 3506  78  19  12 0.01

Run total areal avg QPF for the Central_Greens is: 0.84 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