Each day followed a clear daily cycle in sunlight and temperature. Solar radiation climbed from zero at night to a peak around midday (often 200–400 W/m² on sunny days, dropping near zero on overcast or rainy days). This drove daytime air temperature increases and nighttime cooling. For example, on Feb 5 the sun pushed air temperature from about -3°C at dawn to +5°C by early afternoon, then back below freezing after sunset. As temperatures rose each day, the vapor pressure deficit (VPD) increased modestly (peaking around 0.5–0.6 kPa on the warmest afternoons), indicating drier air that encouraged more transpiration【14†L61-L64】. After sunset, cooling air raised humidity and VPD fell near 0, often leading to dew formation (leaf surfaces became wet at night). This rhythmic cycle of bright, warmer days and cold, humid nights repeated throughout the period, setting a daily pattern for the tree’s physiology.
Temperatures in early February were relatively mild for winter. Daytime highs ranged from just below 0°C up to +5.4°C (Feb 5), while nights dipped a few degrees below freezing (around -2°C to -3°C most nights). These milder days, combined with moderate sunshine, led to small midday spikes in VPD (~0.3–0.6 kPa), meaning the air could draw some moisture from the tree. However, overall atmospheric demand stayed low – the air was often near saturation at night, limiting excessive needle drying. Wind was gentle in this period (typical breeze <1 m/s, with only light gusts ~2–2.5 m/s), so there was little extra drying or mechanical stress on the fir.
Precipitation came as several light rain (or wet snow) events on Feb 8, 9, and 10, totaling about 2.45 mm over the three days. Notably, on Feb 8 late afternoon a quick shower fell (~0.4 mm in an hour), and on Feb 10 around midday a brief downpour occurred (peak ~0.27 mm in 15 min, equivalent to ~14 mm/h intensity at its heaviest). These rains significantly moistened the soil. The soil volumetric water content rose from ~0.38 m³/m³ (early Feb) to about 0.41 m³/m³ by Feb 10, indicating the soil was nearing field capacity. The soil matric potential stayed very high (around -0.3 to -0.8 kPa, close to 0), meaning the soil water was held with almost no tension. Such wet soil conditions make water readily available to roots, far above the stress threshold (for context, plants only begin wilting around -1500 kPa【17†L102-L110】). Each rain event was followed by an uptick in soil moisture and only a minimal, temporary drop in VPD (rain brings humidity), so the tree consistently had ample water. Overall, this period gave the fir a good water recharge with moderate warmth – a low-stress interval where the tree likely experienced minimal stress and even some mid-winter growth or photosynthesis on the sunnier days.
After Feb 10, the weather turned dry and increasingly cold. From Feb 11 through 20 there was virtually no precipitation (only a trace 0.03 mm on the 21st early morning). Under continued clear skies, soil moisture gradually drained from ~0.41 back down to ~0.38 m³/m³ by Feb 20 as no new water was added. Even at 0.38 the soil remained fairly moist, and matric potential stayed around -0.5 kPa, so drought stress in the root zone was still absent. Daytime sun continued (many clear days with solar peaks >300 W/m²), but without new rainfall the air and soil began to dry slightly. Interestingly, as the air grew colder, its absolute moisture capacity dropped – midday VPD values during this dry period remained low (generally <0.3 kPa), because cold air simply cannot hold much vapor. Thus, even though there was no rain, the low temperatures kept atmospheric moisture demand modest, preventing any severe drying of foliage.
The critical story in mid-February was the extreme cold wave. Around Feb 14–17, a polar air mass settled in: temperatures plummeted to the lowest of the month. The fir endured nighttime lows around -10°C on Feb 15–18 (bottoming at -10.1°C on Feb 17), and even daytime highs stayed well below freezing (only -5 to -4°C on those days). This prolonged freeze is a classic cold stress event for any plant. The tree’s metabolism would slow, and any exposed tissues faced frost damage risk. Fortunately, conditions that often worsen freeze injury – intense sun and wind – were moderated. While there was some sunshine (e.g. Feb 16–17 had clear skies), the frigid air held very little moisture, so relative humidity stayed high and VPD hovered near 0. On Feb 15, for instance, midday VPD was effectively 0.0 kPa despite sunshine, indicating the air was fully saturated and not pulling water from needles. Additionally, winds were generally calm during the cold snap (typical gusts under 1–2 m/s). This helped the fir because winter sun and wind together can cause excessive needle water loss when roots are in frozen soil【11†L218-L221】. In our case, the soil temperature at 10 cm depth remained just above freezing (~1°C), so the ground wasn’t completely solid. The fir’s roots likely could still uptake some water, or at least the soil’s high moisture content provided a buffer. Thus, while the tree endured severe freezing temperatures, the lack of drying winds and the humid, calm air meant it probably avoided the worst of winter desiccation. The main stress here was cold injury potential (frost burn to needles or buds and bark contraction). By Feb 18–20, the cold eased slightly (highs creeping toward 0°C, nights around -6 to -9°C), marking the end of the deep freeze. The fir would have been dormant but stable through this period – a test of its frost hardiness, with thankfully no additional water stress factors compounding the cold.
Starting Feb 21, a pronounced warming trend took hold along with a return of wet weather. Temperatures climbed above freezing by day and even at night towards the end of this interval. By Feb 22, afternoon highs reached +4°C and on Feb 24 the air hit +6.1°C – the warmest during this span. Nights, which had been subzero all month, suddenly stayed just above 0°C from Feb 23 onward (e.g. min +2.1°C on Feb 24). This thaw would have started melting any snow or ice around. The fir transitioned from bitter cold to milder conditions in just a few days, a change that can cause some strain (for instance, rapid expansion of frozen tissues or loss of winter hardiness). However, it also meant a relief from frost stress and a chance for the tree to rehydrate and resume metabolic activity modestly.
Moisture returned in force: after 10 dry days, a series of rain events soaked the region. It began with light rain on Feb 22 (~0.9 mm total that day), followed by a brief lull on the 23rd (daytime was mostly dry). Then on Feb 23 late evening, steady rainfall set in and lasted through the night into Feb 24. Feb 23–24’s storm delivered the heaviest precipitation of the month – about 2.2 mm on the 23rd (mostly in the evening) and 4.2 mm on Feb 24 (predawn through morning), for a combined ~6.4 mm. Rain fell for hours, sometimes moderately (e.g. intensity peaked ~11.4 mm/h on the 23rd during a heavier burst). By the morning of Feb 24, the soil was nearly saturated with water. Volumetric water content jumped from ~0.38 to 0.409 m³/m³, its highest level, and matric potential rose to ~0 kPa (essentially zero tension, indicating saturation). The fir’s roots now had an abundance of water. In fact, the soil was so wet that it likely temporarily exceeded field capacity. When soil is fully saturated (0 kPa tension), air is displaced from the soil pores, which can suffocate roots if it persists【21†L5-L13】. In this case, drainage was already occurring by Feb 24–25 – the rain stopped by mid-morning on the 24th and the soil would begin draining excess water within a day. Given the moderate rainfall amounts, serious waterlogging stress was probably minor and short-lived. Instead, the net effect was very positive for the tree’s water status: the deep soil moisture recharge ensured the fir had ample reserves going forward.
During the rainstorm, other environmental factors were generally gentle on the tree. The thick cloud cover and rainfall kept solar radiation low (peaking only ~120 W/m² on Feb 23 and ~190 W/m² on Feb 24 when clouds began to break). With the air nearly saturated with moisture, the VPD dropped to almost 0 kPa for long stretches – essentially no evaporative demand on the foliage. The tree was wet from the rain, but in no danger of drying out; if anything, its needles and soil were being hydrated. Winds picked up only slightly during the frontal passage – gusts of 3–5 m/s were observed on Feb 24, which is a mild breeze and well below damaging storm levels. Thus, unlike a violent windstorm, this was a gentle soaking rain event. By Feb 25, precipitation had ceased and some sun reappeared through partly cloudy skies. Midday on the 25th, temperatures were around +5°C with moderate radiation (~170 W/m²). The soil remained very moist (0.409 m³/m³) and VPD stayed low (~0.1 kPa), reflecting moist air and residual humidity from the rains. For the fir tree, this final period was likely a welcome relief: after the preceding deep freeze, the tree now experienced milder warmth and a flush of water availability. Any stress from the sudden change was minimal compared to the benefit of abundant moisture and the end of extreme cold. The tree would be invigorated by the thaw, with its roots well-watered and ready for the coming spring.
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Light and Dark Cycles Every 24 Hours: The fir experienced strong daily rhythms – bright, warmer middays (up to 5–6°C) followed by freezing, humid nights. This cycle meant a daily pulse of photosynthetic opportunity and minor daytime drying, always alleviated each night as temperatures fell and humidity rose. The regular return of near-100% humidity each evening kept the tree’s water loss in check, maintaining a balance in its hydration cycle.
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Periodic Precipitation and Soil Moisture Dynamics: Two main wet periods (Feb 8–10 and Feb 22–24) punctuated the month. Each brought rain that spiked soil moisture and then dry intervals in between saw gradual soil drying. These rains ensured soil water never became limiting. Even after 10 days with no rain (Feb 11–20), soil moisture stayed high enough that the fir never approached drought conditions. When the heavy rain arrived late-month, soil water content hit saturation, providing a full reservoir of water for the tree (with only brief waterlogging risk). We saw clear correlations: rainfall led to immediate increases in soil moisture, and in turn matric potential stayed near 0 (easy water access). Likewise, precipitation events brought down daytime temperatures and VPD (humid air), effectively shielding the tree from water stress while it rained.
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Temperature Extremes – Mild Start vs. Mid-Month Freeze: The tree went from enjoying mild above-freezing days in early February to enduring an Arctic blast in mid-February. During the coldest stretch (Feb 14–18), daily highs remained subzero and lows reached -10°C. This was the most stressful period in terms of temperature. However, mitigating factors (calm winds, very moist air) meant the fir likely avoided the compounded stress of winter desiccation. Soil temperatures just above freezing suggest the root zone wasn’t completely frozen solid, which is crucial – a frozen root zone can lead to foliage desiccation when sunny【11†L218-L221】. In this case, the fir’s foliage still faced extreme cold, but at least it wasn’t simultaneously starving for water. By contrast, late in the month the pendulum swung to unseasonable warmth – with nights turning mild and a significant thaw. This rapid warming was a sharp change, but it relieved cold stress. The fir may have begun de-hardening or preparing for spring by the 25th, benefiting from the gentler conditions.
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Vapor Pressure Deficit and Transpiration: VPD remained generally low (mostly under 0.5 kPa) throughout, reflecting the cool temperatures and periodic humidity. On the few warmer, sunny days (e.g. Feb 5, Feb 19), midday VPD crept up, which would increase transpiration demand on the fir’s needles【14†L61-L64】. Yet even the peak VPD (~0.6 kPa) was modest – high VPD in summer can exceed 2 kPa for comparison. Whenever the tree encountered higher VPD afternoons, it still had plenty of soil moisture to draw from, so it likely met its water needs without strain. During rains and cold foggy weather, VPD dropped to essentially zero, meaning transpiration nearly stopped. In short, the tree’s water loss was well in balance with water supply this month, avoiding drought stress.
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Wind and Storm Events: No severe wind storms occurred in this period. The strongest gust recorded was ~5.3 m/s (on Feb 12) – a modest breeze that poses little threat to a mature fir. Most of the time winds were calm or light. This spared the tree from mechanical stress (no broken branches or excessive sway) and also reduced wind-driven evaporation. The significant weather events were precipitation-driven rather than wind-driven. For instance, the late-month rain was steady but not accompanied by high winds or lightning (no lightning activity was noted). Thus, the fir did not face any windstorms or physical damage events; its environmental challenges came more from temperature swings and moisture variation than from gale-force winds.
In summary, the fir tree experienced a month of dynamic winter conditions: a mix of mild spells, a deep freeze, and a soaking rainstorm. Each “story” in the data – from the early February rains that kept it watered, to the mid-February freeze testing its cold tolerance, to the late February thaw and rains recharging its roots – played a role in the tree’s health. Thankfully, none of these events appear to have pushed the fir beyond its stress limits. The soil never dried out, the coldest days were paired with forgiving humidity, and the heavy rains came without damaging winds. The fir likely emerged from February in good shape: well-hydrated, structurally intact, and hardened by the cold, ready to take advantage of the coming spring growth period.